My friend has been having a very strange problem. Whenever he plays Diablo 3 or DoTA 2 online using his Nvidia gtx 460, his internet disconnects after about 15-20 minutes of playing. This only happens with this card, as he also has a Nvidia 9500 gt that never gives him any problems. He has everything up to date, his graphics card, network card, motherboard, etc all have the latest drivers. He's tried port forwarding and all that but again, it ONLY happens with his gtx 460, he can play the games with his 9500 gt just fine, albeit not as smoothly. Any ideas as to what's causing this? His motherboard is a Gigabyte g31m-es2L if it helps.
As mentioned above, the PSU is more than likely the cause, this chart shows the recommended PSU watts for a 460 is 500w and the 9500 is 350w.
Even though his PSU is a 550w it is probably not supplying 500w. With cheap PSU's the power output decreases over time due to cheap components. I would start with replacing this, if he can borrow one from someone else to test with it may save him money buying one and finding out that it is not the problem.