I just accidentally downloaded a nasty virus. When ran, it installed itself and shut the computer down. When I tried to start it up again, a blank screen appeared after Vista's loading bar, and before the welcome screen and Vista logo. When I go into safe mode, the computer crashes with a blue screen after a minute. I managed to disable all services and processes in msconfig before it crashed, but it still does the same thing.
After some more googling, I tried pressing Alt-Tab, and 2 applications came up, both with Vista's default icon. The first didn't have a name, and the other was titled Windows Logon.