Computer *sometimes* loads programs...

I have a Dell Dimension 4100, 933 pentium 3, and i got it new 6 months ago. The only problem i have had with it that sometimes when I try to open Internet Explorer, it doesnt do it. This also happens when I try to burn a CD, sometimes I can get around it, sometimes not. I click on the program from the start, programs list and the arrow goes to an hour glass for a few seconds, then turns back to an arrow, almost as if it tries to open it, but then gives up. Restarting doesnt help this, but if I shut it down and leave it for a long period of time (overnight) and turn it on the next day, it doesnt happen, and everything works fine. But somewhere along the line it just starts doing that again. I dont have problems with any other programs opening that I know of, but if anyone knows whats wrong id greatly appreciate it!
Thanks, Phil