Using ATITool, I let it slowly try and find an OC for the vid card. There was some improvement in test scores. Then, when the room became 12 degrees C cooler due to wintertime and an open window, I thought I would try again. Except I manually specified a GPU/RAM clock of 600/600. That soon crashed. I tried to take advantage of the temporary frigid conditions in a lab sense. I would never leave the card set to that once testing was done and room window closed. I let 3DMark06 have a go at it and left the room. When I returned a short while later (room still frigid) I found my booting BSOD's, and the mirrored HD array partition table was borked. Fortunately the data was still OK on the 2 drives. I copied one drive to an empty one, reformatted the array with a fresh copy of Win XP SP2, as before, and have started to restore apps/games via re-installation from app/game media. My PC and Radeon are running at stock speeds. Radeon was purchased 2005-June. Before the experiment, I had been running a 30% CPU overclock, with no Radeon OC. The Radeon worked flawlessly with everything. Current Observations: vid card passes all 4 Futuremark, Aquamark benchmarks with reasonable scores Windows doesn't have any visible glitches at 1600 x 1200 Unreal Tournament 2004 now crashes at the game type menu with monitor losing sync and stuttering sound - reboot needed BF 1942 does the same F.E.A.R. soon crashes after a few minutes of play Nanosaur Hatchling plays ok (great game BTW) regular video files play OK - I.E. Windows Media Player, PowerDVD TV card is OK vid card fan goes to high for a few seconds after normal PC boot, which is normal, then resumes almost silent operation everything used to work before I haven't had time to try other 3D games yet. I think I'm using Catalyst driver ~ 5.7. Can anybody suggest a cause or new area of investigation?