I have a ABit BH6 v1.01 running the latest bios "SS". Currently I'm running a Celeron 300A overclocked to 450mzh and 384 megs of RAM under Windows XP Professional. Recently I purchased a ATI Radeon 8500 believing it would function at AGP 2X, but everytime I startup Half-Life, UnReal, and Quake 3 the system locks up then reboots after 3 to 5 minutes of game play. HL locks up the quickest then Unreal and Quake 3 runs the longest. I have the AGP set to 2/3 in the bios and I don't appear to have any resource conflicts. I've tested the ATI Radeon 8500 in an AMD system supporting AGP 4X and it ran without a hitch for 45 minutes. That makes me believe it's something on the BH6 causing the issues.
