I'm having a similar issue as a lot of people in February 2017 with my Lumia 920 with Windows Phone 8.1 after resetting it.

The phone shows the "Keep your life in sync" -welcome page with sign in / create one -buttons but clicking either one only results in the "Can't connect" -popup before asking anything else.

I've tried all the tricks I could find - date and time settings are correct and system updates checked but I'm still not able to add an existing Microsoft account or try to create a new one. The Internet connection works fine, I can access live.com and use my Hotmail with the phone's browser.

EDIT: This apparently got silently fixed as I was able to sign in on my Lumia 920

Spam/Advertising/Phishing, and Scam Virus/Spyware/Malware danger Other Term of Use or Code of Conduct violation Hate Speech and Discrimination Suicide or self-injury Child exploitation or abuse Harassment is any behavior intended to disturb or upset a person or group of people. Threats include any threat of violence, or harm to another. Any content of an adult theme or inappropriate to a community web site. Any image, link, or discussion of nudity. Any behavior that is insulting, rude, vulgar, desecrating, or showing disrespect. Any behavior that appears to violate End user license agreements, including providing product keys or links to pirated software. Unsolicited bulk mail or bulk advertising Any link to or advocacy of virus, spyware, malware, or phishing sites. Any other inappropriate content or behavior as defined by the Terms of Use or Code of Conduct. Hateful content that attacks, insults, or degrades someone because of a protected trait, such as their race, ethnicity, gender, gender identity, sexual orientation, religion, national origin, age, disability status, or caste. Any content about suicide and self-harm that could be dangerous. Any image, link, or discussion related to child pornography, child nudity, or other child abuse or exploitation.

same error but on Lumia 735

Update 07/04/2017 - Now logged back in and re-downloading windows 10.

Would of been nice for Microsoft update on this though.

Spam/Advertising/Phishing, and Scam Virus/Spyware/Malware danger Other Term of Use or Code of Conduct violation Hate Speech and Discrimination Suicide or self-injury Child exploitation or abuse Harassment is any behavior intended to disturb or upset a person or group of people. Threats include any threat of violence, or harm to another. Any content of an adult theme or inappropriate to a community web site. Any image, link, or discussion of nudity. Any behavior that is insulting, rude, vulgar, desecrating, or showing disrespect. Any behavior that appears to violate End user license agreements, including providing product keys or links to pirated software. Unsolicited bulk mail or bulk advertising Any link to or advocacy of virus, spyware, malware, or phishing sites. Any other inappropriate content or behavior as defined by the Terms of Use or Code of Conduct. Hateful content that attacks, insults, or degrades someone because of a protected trait, such as their race, ethnicity, gender, gender identity, sexual orientation, religion, national origin, age, disability status, or caste. Any content about suicide and self-harm that could be dangerous. Any image, link, or discussion related to child pornography, child nudity, or other child abuse or exploitation. Spam/Advertising/Phishing, and Scam Virus/Spyware/Malware danger Other Term of Use or Code of Conduct violation Hate Speech and Discrimination Suicide or self-injury Child exploitation or abuse Harassment is any behavior intended to disturb or upset a person or group of people. Threats include any threat of violence, or harm to another. Any content of an adult theme or inappropriate to a community web site. Any image, link, or discussion of nudity. Any behavior that is insulting, rude, vulgar, desecrating, or showing disrespect. Any behavior that appears to violate End user license agreements, including providing product keys or links to pirated software. Unsolicited bulk mail or bulk advertising Any link to or advocacy of virus, spyware, malware, or phishing sites. Any other inappropriate content or behavior as defined by the Terms of Use or Code of Conduct. Hateful content that attacks, insults, or degrades someone because of a protected trait, such as their race, ethnicity, gender, gender identity, sexual orientation, religion, national origin, age, disability status, or caste. Any content about suicide and self-harm that could be dangerous. Any image, link, or discussion related to child pornography, child nudity, or other child abuse or exploitation. Spam/Advertising/Phishing, and Scam Virus/Spyware/Malware danger Other Term of Use or Code of Conduct violation Hate Speech and Discrimination Suicide or self-injury Child exploitation or abuse Harassment is any behavior intended to disturb or upset a person or group of people. Threats include any threat of violence, or harm to another. Any content of an adult theme or inappropriate to a community web site. Any image, link, or discussion of nudity. Any behavior that is insulting, rude, vulgar, desecrating, or showing disrespect. Any behavior that appears to violate End user license agreements, including providing product keys or links to pirated software. Unsolicited bulk mail or bulk advertising Any link to or advocacy of virus, spyware, malware, or phishing sites. Any other inappropriate content or behavior as defined by the Terms of Use or Code of Conduct. Hateful content that attacks, insults, or degrades someone because of a protected trait, such as their race, ethnicity, gender, gender identity, sexual orientation, religion, national origin, age, disability status, or caste. Any content about suicide and self-harm that could be dangerous. Any image, link, or discussion related to child pornography, child nudity, or other child abuse or exploitation. Spam/Advertising/Phishing, and Scam Virus/Spyware/Malware danger Other Term of Use or Code of Conduct violation Hate Speech and Discrimination Suicide or self-injury Child exploitation or abuse Harassment is any behavior intended to disturb or upset a person or group of people. Threats include any threat of violence, or harm to another. Any content of an adult theme or inappropriate to a community web site. Any image, link, or discussion of nudity. Any behavior that is insulting, rude, vulgar, desecrating, or showing disrespect. Any behavior that appears to violate End user license agreements, including providing product keys or links to pirated software. Unsolicited bulk mail or bulk advertising Any link to or advocacy of virus, spyware, malware, or phishing sites. Any other inappropriate content or behavior as defined by the Terms of Use or Code of Conduct. Hateful content that attacks, insults, or degrades someone because of a protected trait, such as their race, ethnicity, gender, gender identity, sexual orientation, religion, national origin, age, disability status, or caste. Any content about suicide and self-harm that could be dangerous. Any image, link, or discussion related to child pornography, child nudity, or other child abuse or exploitation. I just got my lumia 920 out of my drawer and I had to reset my phone (all data erased), after that I couldn't open the store and I couldn't add a microsoft account. I just downloaded "Windows Device Recovery Tool" and it said the firmware version was too old. Now it's updating it -it will again erase all data on the phone- and hopefully it will work. You could try this as well. Spam/Advertising/Phishing, and Scam Virus/Spyware/Malware danger Other Term of Use or Code of Conduct violation Hate Speech and Discrimination Suicide or self-injury Child exploitation or abuse Harassment is any behavior intended to disturb or upset a person or group of people. Threats include any threat of violence, or harm to another. Any content of an adult theme or inappropriate to a community web site. Any image, link, or discussion of nudity. Any behavior that is insulting, rude, vulgar, desecrating, or showing disrespect. Any behavior that appears to violate End user license agreements, including providing product keys or links to pirated software. Unsolicited bulk mail or bulk advertising Any link to or advocacy of virus, spyware, malware, or phishing sites. Any other inappropriate content or behavior as defined by the Terms of Use or Code of Conduct. Hateful content that attacks, insults, or degrades someone because of a protected trait, such as their race, ethnicity, gender, gender identity, sexual orientation, religion, national origin, age, disability status, or caste. Any content about suicide and self-harm that could be dangerous. Any image, link, or discussion related to child pornography, child nudity, or other child abuse or exploitation. You still will not be able to access the Store, because it closed on December 16th 2019. At present there is a global issue with WP8.1 devices unable to set up or log in to a MS account - whether this will be fixed I don't know but it is quite possible that MS will no longer bother to do it given that support for WP8.1 ended in July 2017.
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"Remember that a lone amateur built the Ark. A large group of professionals built the Titanic." Spam/Advertising/Phishing, and Scam Virus/Spyware/Malware danger Other Term of Use or Code of Conduct violation Hate Speech and Discrimination Suicide or self-injury Child exploitation or abuse Harassment is any behavior intended to disturb or upset a person or group of people. Threats include any threat of violence, or harm to another. Any content of an adult theme or inappropriate to a community web site. Any image, link, or discussion of nudity. Any behavior that is insulting, rude, vulgar, desecrating, or showing disrespect. Any behavior that appears to violate End user license agreements, including providing product keys or links to pirated software. Unsolicited bulk mail or bulk advertising Any link to or advocacy of virus, spyware, malware, or phishing sites. Any other inappropriate content or behavior as defined by the Terms of Use or Code of Conduct. Hateful content that attacks, insults, or degrades someone because of a protected trait, such as their race, ethnicity, gender, gender identity, sexual orientation, religion, national origin, age, disability status, or caste. Any content about suicide and self-harm that could be dangerous. Any image, link, or discussion related to child pornography, child nudity, or other child abuse or exploitation. Yeah I just actually realised that 2 hours ago. We won't even be able to have any apps anymore becase they left supporting Store for windows phone 8.1. I hadn't touched this phone since 2016 because all other lumia phones were getting windows 10 update but mine wasn't, and this result is not at all unexpected. Microsoft never learned how to handle mobile devices. Spam/Advertising/Phishing, and Scam Virus/Spyware/Malware danger Other Term of Use or Code of Conduct violation Hate Speech and Discrimination Suicide or self-injury Child exploitation or abuse Harassment is any behavior intended to disturb or upset a person or group of people. Threats include any threat of violence, or harm to another. Any content of an adult theme or inappropriate to a community web site. Any image, link, or discussion of nudity. Any behavior that is insulting, rude, vulgar, desecrating, or showing disrespect. Any behavior that appears to violate End user license agreements, including providing product keys or links to pirated software. Unsolicited bulk mail or bulk advertising Any link to or advocacy of virus, spyware, malware, or phishing sites. Any other inappropriate content or behavior as defined by the Terms of Use or Code of Conduct. Hateful content that attacks, insults, or degrades someone because of a protected trait, such as their race, ethnicity, gender, gender identity, sexual orientation, religion, national origin, age, disability status, or caste. Any content about suicide and self-harm that could be dangerous. Any image, link, or discussion related to child pornography, child nudity, or other child abuse or exploitation. Spam/Advertising/Phishing, and Scam Virus/Spyware/Malware danger Other Term of Use or Code of Conduct violation Hate Speech and Discrimination Suicide or self-injury Child exploitation or abuse Harassment is any behavior intended to disturb or upset a person or group of people. Threats include any threat of violence, or harm to another. Any content of an adult theme or inappropriate to a community web site. Any image, link, or discussion of nudity. Any behavior that is insulting, rude, vulgar, desecrating, or showing disrespect. Any behavior that appears to violate End user license agreements, including providing product keys or links to pirated software. Unsolicited bulk mail or bulk advertising Any link to or advocacy of virus, spyware, malware, or phishing sites. Any other inappropriate content or behavior as defined by the Terms of Use or Code of Conduct. Hateful content that attacks, insults, or degrades someone because of a protected trait, such as their race, ethnicity, gender, gender identity, sexual orientation, religion, national origin, age, disability status, or caste. Any content about suicide and self-harm that could be dangerous. Any image, link, or discussion related to child pornography, child nudity, or other child abuse or exploitation. Spam/Advertising/Phishing, and Scam Virus/Spyware/Malware danger Other Term of Use or Code of Conduct violation Hate Speech and Discrimination Suicide or self-injury Child exploitation or abuse Harassment is any behavior intended to disturb or upset a person or group of people. Threats include any threat of violence, or harm to another. Any content of an adult theme or inappropriate to a community web site. Any image, link, or discussion of nudity. Any behavior that is insulting, rude, vulgar, desecrating, or showing disrespect. Any behavior that appears to violate End user license agreements, including providing product keys or links to pirated software. Unsolicited bulk mail or bulk advertising Any link to or advocacy of virus, spyware, malware, or phishing sites. Any other inappropriate content or behavior as defined by the Terms of Use or Code of Conduct. Hateful content that attacks, insults, or degrades someone because of a protected trait, such as their race, ethnicity, gender, gender identity, sexual orientation, religion, national origin, age, disability status, or caste. Any content about suicide and self-harm that could be dangerous. Any image, link, or discussion related to child pornography, child nudity, or other child abuse or exploitation.