Media Players presenting odd behaviours

Hey guys,

My PC is an AMD 64-bit Athlon 3700+ running with:

2GB Kingston DDR 400mHz RAM
600W fan
GeForce 4 7600 XFX 4xAGP

I've recently been experiecing 'graphical errors' with Medieval 2 and sought Tech Help on related forums, answers consisted of re-installing graphics drivers, and updating DirectX.

Since doing both of these my game is experiencing jerkiness, even the movie in the background of the main screen. (Yet others such as Source related games are WoW aren't an issue.)

I thought this was the extent of my problems, but as of last night I noticed when I tried to watch an episode of a TV program using Windows Media Player, my monitor turned off, turned on again, then turned off before closing WMP without an error, resulting in excessive slow-down speeds of my PC. Restarting the PC fixes this.

I tried again using Quick Time, and the window for quicktime itself took a while to construct itself across the screen and sent my PC whirring, and was very very slow. Even acessing process manager to shut it down was a slow-paced hassle. (However once it's closed, the PC is back to normal.)

I've ran Spybot Search & Destroy, Hijack This and AdAware which have found nothing out of the ordinary with regards to viruses so I don't know what's happening.

Can anybody help me? :S

- Heskey