Cannot play movie files

I have a friend thats got a big problem. his computer dislikes movie files. In other words it completely freezes up as soon as he tries to run a movie file. like avi mpeg etc. Any streaming video etc locks it up. Ingame videos run fine and so do music files. He has installed all the latest codecs and the latest media players but still nothing. He is running a

Windows XP Home SP2
AMD sempron 2500
geforce 6600
512mb ddr400 pc2700
60Gb hard drive

Any clues on y the pc is freezing up and any ideas on how to resolve the problems? Thanx all in advance!

 

Hi
As you havent had any other replies I would suggest that, following defragmenting the hard drive your friend makes sure he has the latest video card drivers from the website, and then download the klite codec pack (which is free, although some websites try to make you pay for it).
Regards
steve