Originally Posted by oldcpu
Some notes - the Athlon-1100 PC in which this runs has a 350 watt original power supply, and is 9 years old. The BFG 8400GS card requires a 300 watt power supply. I assume the power supply is still adequate after 9 years. I note same problem with desktop graphic corruption does not occur with VESA driver hence giving me faith in power supply. There is no evidence of over heating in the PC, as fans are clean and functioning well.
Your assumptions may not be valid. Due to capacitor degradation with time your motherboard may be drawing more power than it once did, for the same reason the power supply may not be able to provide as much power as before (or less clean power at higher wattage). The VESA driver may not push the graphics card nearly as hard as the Nvidia driver. I once had a set of computers with power supply capacity "on the edge", these ran fine up until SpecViewPerf started, when some of them would crash. The fault moved around with the power supplies. They were all apparently within a few percent of capacity, some just over, some just under. In that case adding a single 80mm case fan was enough to switch some machines from working with SpecViewPerf to not working. Similarly, unplugging all the case fans on some of those that were failing was enough to get them working again.