|What happened to the computer between the last time it worked OK and the first time it didn't?|
I think that's a Dell message and not from the OS:
At the c:\> prompt type WIN and hit enter. If you get 'bad command or file name' try typing DIR/P and enter at the prompt. That will scroll through the files and directories on the root drive one page at a time. Do you see a 'windows' directory?
Real men don't use AntiVirus; they just reformat