Ok not my computer, its a friends so god only knows what she did to it.
But she told me out of no where when she turned it on, windows prompted for a user name/password
suspicious thing is that when it ask for login credentials the user name is blank and there is no user picture. There is no welcome *name*.
So can this be a virus?
And anyway to get into windows. I know or heard of password crackers. But not sure if it will work when the username is unknown or null.
Most likely it is an infection. Try Vista recovery options.http://windows.microsoft.com/en-US/windows-vista/What-are-the-system-recovery-options-in-Windows-Vista
Or booting into safe mode to see if you can run AV scan.