Pci-e bus failure

Not sure where this belongs and I have only limited info. Trying to help a buddy in Australia - I'm in California.

His system is an older one, not sure which mobo but he runs a p4 3.4 with 1Gram and NVidia 5200 256M AGP card.

System ahs been stable for quite a while but during the last few weeks, when he runs Flight Simulator X or Flight Simuolator 9, the system will shut down after 10 minutes. Had him remove the side, blow out all the fans, etc. Still happening.

He ran the nvidia ntune program and it failed the PCI-e bus and the GPU test in 1m 45seconds. Remember this is an AGP card.

FSX and/or FSP really stress the CPU, GPU and the memory subsystem.

He can run any of his other stuff all day long with no problems, but either FS program and crash in 10.

He's retired and I'd hate to have him spend $$ on a new video card when the mobo is bad. I can see the vid card overheating but what would that have to do with pci-e bus failure UNLESS the CPU and or tyhe mobo is overheated or failing also?

There are some test suites that I know of but I doubt he could get them configured properly.

Appreciate any thoughts.

Vic