This is the explorer bug I have had since...forever. I am running Windows NT 5.1 Corporate (XP SP2) build 2600.
The effects of this bug are as follows:

Elements disappear
No right-click
Left click works, but doesn't do anything
Won't open new programs or windows
Programs throw up random errors
Restores more than one window at the same time
Screen saver doesn't work
Programs can't be closed or terminated if they're unresponsive
When web browsing, a new page won't load, or the screen will turn black
Programs can't be minimized, but they can be restored or maximized
No popup descriptions, or they aren't displayed properly
Sometimes gets triggered by Shareaza (wtf?)

I can stop this from happening temporarily by closing two windows, it doesn't matter what they are. 
But the bug comes back again and again every couple of minutes and gets more annoying until I eventually need to reboot (if I have nothing else to close).

I ran XPY over the fresh install, as it was ALREADY slow, I didn't like it so I reversed the changes, but these changes still remained:

Programs won't group
Quick Launch gets reset every reboot
No user image in start menu
No welcome screen, which does make boot faster, but switching users annoying

What I have done to fix the problem:

Re-apply the service pack
Reinstall
Format and reinstall
Install on a different hard drive
Install it on a new computer

And it still happens...

Another problem, which may or may not be related is my sound card: Occasionally it will produce two very loud and distinct clicks about one second apart, every couple of minutes. I've ruled out my amp because it still happens when I mute with the keyboard, but not the amp itself.

I think it might be faulty RAM/motherboard. I did have an incident where something shorted between the graphics card and the motherboard (probably some dust with conductive crap on it) and very literally blew up the power supply. The motherboard and graphics card survived, but I think that's when the sound card clicks started.