Comp freezes after 3 repeat missions

This happens every day (or night). I boot up and enter GW. I do a long mission like Borlis Pass and don't quite make the end before everyone dies..no problems.
Repeat the same..no problems, but on the 3rd attempt, halfway thru' my comp will start lagging and then 10 mins later it freezes. I have to bail out. I get the feeling that it runs out of memory. The game, at full graphics, runs great..no lag..no stuttering. Any suggestions ?

2.8 cpu
1 gig DDR Ram
ATI Radion 6800 video card
Wireless internet connection which never gives me any problems.
No Teamspeak.
Similar story to The Paresha post.

Thanks..Dr Wu

Try re-installing GW. If not, its your video card. You should get a new one.

Possibly overclocked too high? If you overclocked your gfx card or cpu (depending on type of cpu) you might want to check if your running it to high.