This has been happening for the past few weeks now. It usually happens after a few hours of inactivity on the computer. I let it download and seed stuff on BT.
Before, I received an Explorer runtime error..
Which resulted in a crash of programs and the inability to open a folder window.

A few minutes ago when I got back on from leaving the computer inactive, the same thing happened..
Except it didn't give me a pop-up error.
My ZoneAlarm firewall had a huge X on the system tray icon(bottom right) too.
It cannot shut down unless I push the external power button.
I cannot open a new window or the task manager.. or any program from a shortcut.
This continues to happen before and after I installed the new IE.

This happens frequently.

I use:
Windows XP Pro SP2 updated with the most recent updates
NOD32
ZoneAlarm Basic
PG2
uTorrent
MaxMem