If you are unable to add your existing Microsoft account or create a new account, try the following:
- Check the phone date and time. Go to Settings > Date+time and manually set the correct time zone, date and time. Try signing in again.
- If the above action doesn't solve the problem, connect to a Wi-Fi network and try signing in via that network.
- If the issue still persists, reset your phone in Settings > About > Reset your phone and run the setup wizard again. Be sure to set the correct date and time before trying to sign in with your Microsoft account.
Adding the Microsoft account may fail if the phone date is not correct. It may also fail if the network connection is not working properly or if the phone has got into a state where it needs to be reset.
When the date is wrong or the Microsoft account is missing, you may not be able to download the apps from the Store.
If still not able to add your account, check that your Microsoft account is working properly by using a PC browser to sign in.