Recently, I've got a new XFX NVIDIA GeForce 6200 256Mb DDR2 TV DVI from a store at $43. I have inserted it into my old system:
AMD Duron (Applebred) 1.4GHz (overclocked to 1.8GHz)
VIA KM400 Northbridge Chipset
512Mb DDR-400 SDRAM
Western-Digital 60Gb 7200RPM EIDE HDD
WinXP Home 32-bit SP2
NVIDIA GeForce4 MX440 AGP8X (before)
When installed, I tried to run MoH Pacific Assault & Call of Duty 2 on the new graphic card. It worked, but sometimes it stopped working. I need to reset it to get everything back to normal. When I tested using DirectX Diagnostic Tool under Display tab, the tests did not completed properly (the DirectX cube sometimes spinning sometimes not). Everything went well under my previous graphic card (GeForce4 above).
Check your card is not overheating, enough case cooling ??.
Some systems need the latest drivers for the AGP/PCI express bus, try auto update or manually check...use the latest graphics driver also (nvidia.com)