Recently, my PC with Windows Vista Home Premium completely lost the login screen. It was turned off for the night and the next day all it was was a black screen with no profiles to sign into.All I get it a black screen with the mouse on it.

I had a computer person come and try to fix it, and they were completely baffled for like 3 hours. Anyone have any ideas on how I can get into the computer? It just won't work because there's not login screen. ;(