Inspiron 1420 not opening programs, not shutting down, running sluggishly

My Dell Inspiron 1420 (Vista SP 1) suddenly started running sluggishly after I woke it up out of hibernation yesterday. It won't open programs such as System Restore and MSWord, but it runs Firefox and CCleaner without a problem. Task Manager shows up in the tray but won't open as a window.

It also locks up when I try to shut it down, and I've had to force it manually. It boots up fine.

I've defragged recently, cleaned the registry, cleaned out temp files, run scans with SpyBot. Then I followed the instructions on the malware removal guide in this forum, and nothing seems to have changed.

Also, I don't know if this is relevant, but two new processes try to run at every start-up: "apntex.exe" (which I understand to be related to the touchpad driver) and "services.exe".

Thank you for any advice you can give me!