As part of the troubleshooting process, I backed off on my up-to-date Via 4-in-1 drivers v4.40 and re-installed v4.35 on advice from the via forums. Whenever a new video card is installed on this mobo, or the drivers change, it always installs in windows at AGP2X, regardless of the bios settings. There is a registry key supplied by Asus support that they claim is a "Windows AGP 4X turn-on key". This key is named "ViaAgp4x.reg". It's content is[HKEY_LOCAL_MACHINE\Software\NVIDIA Corporation\Global\System]"EnableVia4x"=dword:00000001. Indeed when this key is inserted, windows, card properties, and 3dmark all report 4X as being enabled. This is suspect however, because with 4X enabled in bios, my 3dmark 2001 reported a speed of 6875 before the key change and 6889 after, so it certainly makes hardly any difference speed wise. With this key in the registry however, the mysterious locking issue occurs on all game re-loads. If I change the key's last digit to 0, everything reports AGP2X and all games run perfectly. I tested GTA3 for several hours continuously with no problems at all. It appears that the "turn-on key" is not much more than "window dressing" and certainly borks the system. Whether or not this board actually runs at 4x is anyone's guess, but it certainly won't run anything but 3dmark with this registry key turned on. Now that it actually works, I'm off to tweak land to try and raise scores in 3dmark, but since that test is so easy to fool, maybe I'll just enjoy some of my games first! Thanks to all, and I hope this info may help someone else saddled with a Via chipset.