Graphics problem?

[Jonny]

My PC is working fine when idle, or just internet/iTunes/office apps etc, but when I start to play a game, it will work fine for up to 5 minutes, but then will lock up, and do one of 3 things: return to the Windows desktop and say no more, reboot itself, or simple stay locked up. There are also occasions when it will lock for 15 or 20 seconds and then continue like nothing had happened, but then may lock up later on.
Sometimes, when it reboots, there will be bands of thin white lines running vertically down the screen.
This happens on Far Cry and Doom 3, but not Live For Speed.
It's a year old Radeon 9800 Pro that was previously in another system. I am running an old (2001) Relisys monitor at 85Hz, with a 1024 res.
Nothing is overclocked (any more).
Any ideas?

[Ferral]

Sounds like it may be overheating, check the cooling on it and make sure the fan is clean and oiled.

Other than that try knocking the AGP down to 4x and see if it works, some motherboards dont like Radeons at 8x AGP and cause lockups etc, might actually be worthwhile trying this one first.

[unrealuniverse]

Like ferral said it seems to be overheating. radeon cards with stock coolers run hot anyway. if the fan is starting to go on the card or there is a lack of airflow in your case then this may be enough to cause these problems.

easy solution is to run the computer with its side off and see if it still crashes, if it does then it isn't overheating.

[Jonny]

Ok, giving the whole system a thorough clean and tidy. Removed dust filters and cleaned fan on the Radeon. I'll let you know how I get on.
Thanks