My Boss’s PC boots into XP Pro fine but after logging in the only thing he
sees is the wallpaper. The same happens for any other user. His Vista
installation runs fine but he still needs XP for other things right now. XP
was the first OS installed on the machine and neither OS is virtualized.

I can open programs and such through the task manager but running
explorer.exe will bring up the taskbar for maybe a split second before it
disappears again. Explorer.exe doesn’t appear in the process list.

Virus scans came out clean, and his machine is fully patched. A repair
installation had no effect.
I also ran some script off a website I don’t remember that’s supposed to
bring back the taskbar in I guess a similar situation but this had no affect
either. Explorer.exe just crashes as soon as it is run.

Any ideas what could be wrong or how to fix it?