Re: stuck on samsung account screen
If the account shows up in your settings try removing it from there and trying to re-add it. You can also try to clear the device's cache (NOT data, as this will wipe out your device...just cache, this deletes temporary files) by booting up your phone into Recovery Mode.
You can try changing your password on the website and trying again, with the new credentials, on your phone. Again, make sure you have a valid Internet connection.
I'm curious, if you input a bad password, do you get an error on your phone?