DVD freeze

All DVDs when played on my copmuter freeze after 4-5 minutes of playback. The image freezes but the sound continues. The only way to get the image to update is to reopen the software.
It is not a problem with the DVD or the player (i have tried many).
I am running:
AMD sempron 2600+
512meg ram
gforce fx 5200 128meg
Windows XP
this is driving me mad! help..?
Alex