I found this one before and it was caused by a keyboard logger. The tip-off was some functions stopped working. There are many such pests, so get a second opinion virus scan with Housecall. The person didn't believe it was a virus since "I have Norton."
You could boot a dos disk (http://www.bootdisk.com) to see if that worked with control-alt-del.
Hardware: Compaq Evo 410c
OS: Windows XP Professional
Recently, my Compaq Evo 410c notebook stopped recognizing Ctrl-Alt-Del. Each of these keys work individually, but the combination is not recognized (you know what a pain it can be trying to login to Windows). I've managed to get around this by disabling the requirement for pressing Ctrl-Alt-Del to get the username/password dialog.
Now the "Fn" key has stopped working. None of the controls, like switching the video output (Fn+F4) or brightness control etc., work.
The only changes to my system have been Windows XP security patches. I have no known viruses and my definitions are up to date. I've also tried changing the default keyboard driver from MS to Compaq - but things are the same.
Could anyone suggest what I could possibly do? Maybe some hardward diagnostics that's independent of Windows? Or some diagnostic on drivers?