Graphics card overheating?

[Wej]

I've recently built a PC for my daughter with old bits: -

Asus A7N8X motherboard
Athlon 2600+ chip
Radeon 9800 Pro

The problem is, after 5 minutes in any 3d game I start getting graphical corruption and after a while the PC crashes. I've checked temperatures for chip and case but although warm, they seem acceptable. However, could it be that just the GFX card is overheating?

I cleaned the fan on the GFX card and it runs correctly, but I wonder if the heatsink on the card has become loose or something. Is it easy to replace with a bigger heatsink, or is this another problem and the GFX card needs to be replaced?

 

[ACESHIGH]

if it only occurs after some time playing then it may well be a heat issue.
could try a fan blowing onto it if you have one spare to see if it helps other than that a cheap replacement cards probably the go.