Can't close Program windows....

I'm not sure what happened, but no matter what program I am running, (IE, Task Manager, AVG, Registry Tools, Ad-Aware) I can't close the program by clicking on the "x" nor can I close it from Task Manager: once I click on the "x" it doesn't close, and it doesn't show up in Task Manager! If I go to Task Manager and try to close it from there before clicking on the "x" it shows up, but does not close when I click "End Process". The only way to close anything is to restart the computer..... I can open multiple windows, but can't close them once I open them.....

Has anyone ever had a problem like this?

All this started when I was tweaking my desktop, and went to move my daughter's "Blue's Clue's" icon to a folder on the taskbar. This game gave us problems once before, and I promptly un-installed it, and ran Reg cleaners to clear things out. Not sure what other details to give, as I was doing all sorts of tweaking on the desktop, moving "My Pictures" and other stuff.

My Specs:
Windows 2000 Professional
AMD Athlon 1.33
512 DDR
40 Gig Hard Drive
Nvidia GeForce 2 64 MB

Thanks in advance!

Eric