Funkiness with certain programs

Here's my problem: Certain programs will not run any more. This started about a month ago (maybe 1.5 months). I was without internet for about 4 months and then finally got Adelphia cable right before the problems started. The first program to go was Everquest. I could play it just fine, but then it would give me an error when I tried running it. Like, mere seconds after clicking the shortcut it'd say "Everquest has performed an illegal operation". Reinstalling it would fix this (although I'd have to repatch everything).

The next program i noticed was Quicktime. Whenever I try to load a QT movie or just the basic program itself, it thinks for a few seconds and then stops. No error, no nothing. Other programs that don't work include such educational ones as Virtuagirl2 and stripsaver. Same deal; a wee bit of thinking and then it's like I never tried to open the program. Most recently is Gothic 2, and that's what pushed me over the edge; it's a 2.2 gig install so I'm not eager to redo it everytime my computer acts up.

Another problem that has come up recently is everytime windows XP loads, it gives me this full screen report about some problem with Active Desktop, and the only way to get out of it is clicking a hotbutton called Restore Active Desktop. I get this everytime I turn my computer on. I don't use my desktop at all; I have all the icons hidden and never make shortcuts there, so I don't have the foggiest idea why this is going on.

I run Spybot S&D on a regular basis (every 4 days or so) and I really don't do that much surfing/downloading outside of main sites (things like ve3d.com and the like).

My comp specs are athlon 2400, 512 ram, audigy 2, radeon 9500 (non modded) and an asus board which I can't remember the name of (one of the real popular ones, 8gxr or somethin like that).

Thanks for reading this and helping me out.