Xboxlive sign in screen blank

Hi!

Are there any errors on invalid accounts or invalid passwords?

Before adding an account you should clear the system cache with the power cycle system (by holding down the power button for 10 secs). Once the console has restarted, you can proceed to add the profile.

If it doesn't work, you can restore the console to the factory settings by selecting the "Reset and keep my games & apps" option.

hi, do you have a bug in the network settings?

Sorry to hear about your issue.  You said you tried restarting and removing their account.  Lets try a few other things...before you pick up a hammer.  Do a full power cycle of the Xbox.  That means holding down the power button on the console for at least 8 seconds.  Then unplug the console for at least 10 seconds.  Turn everything back on and restart.  If that doesn't fix the issue and you have already removed accounts, you may want to try a factory reset of the Xbox.  It restores the original operating system.  If you do that, select the option that keeps your games and apps so you don't have to re-install all your games.  You will need to know the passwords to your accounts when you start it back up, and you may need to reset any personalized settings you may have added to your Xbox.  There are full instructions on performing a factory reset on the Xbox support webpage.  Let us know if this fixes the issue. 

To add to what has been said. If you can't access the settings via the console, to factory reset, because of the black screen, try these steps.

1. Press and hold console power button for 10 seconds till fully off
2. press and hold both the eject and bind buttons
3. press the power button (keeping bind and eject pressed)
4. wait for second power up chime and release bind and eject
5. you should now see the trouble shoot menu, select reset console
6. select reset keeping all games & apps