He probably had something seriously wrong with his computer before he cleaned it out. Tell him to reboot into safe mode (press f8 repeatedly during a restart). In save mode, go to start, run, and type msconfig. Go to the startup tab and disable everything listed there (except his mouse/keyboard, etc if listed). Then I would recommend he do a defragment. Start, programs, accessories, system tools, defrag. And finally, schedule the system to do a checkdisk at next reboot. He needs to open up explorer and find his C:\ drive. Right click it, choose properties, then tools, and checkdisk. Once he selects checkdisk, have him reboot and let it do its thing. It can take over an hour on a seriously damaged disk but it should fix the bad sectors on his hard drive. After that, tell him to boot into safe mode and run a full virus scan, then defrag one more time. See if that helps.
The funny thing was, though, even in safe mode, it did the same thing as in a normal startup - log him off as soon as it finished loading.
In a case that this, I'd most likely yank the drive, slave it in another machine, recover any work files on the bum drive, format it, and do a clean install.