Go to the link below and under the letter "T" scroll down to "Task Manager - Control/Alt/Delete - Doesn't work" where you'll find several possible fixes.
My task manager wouldn't load up earlyer, so I ran a virus check and restarted and it still wouldn't work, so I system restored to a time when I knew it still worked, and it didn't load up then. Does anybody know why? And if so how to fix it. I have XP Service Pack2