1- Do you have a good strong PSU?
2- Do you have AGP voltage adjustment available on that mobo? Try steppping it up by 0.1V and see what happens - but only after ruling out everything else here.
3- Are you OCing in such a way that it might affect the PCI or AGP clock adversely?
4- Do you have the latest AGP driver installed for your chipset?
5- It looks like something may be stepping on the video BIOS area. Try locking the video BIOS area: addresses A000-C800 so nothing else can use it. You can usually do that in your BIOS setup by "reserving" address blocks. While you're in the BIOS, make sure that the video bios shadowing is DISABLED!
6- Is your video card seated properly?
7- Visit
Adrian's Rojak Pot and check out his BIOS optimizing guide to improve your knowledge of the settings.
Check those out and let me know.
.bh.