I've found that if I've been mining with CGminer, which OCs my 6950 to 880/1350 and never gives any HW errors and then stop it and play a game, it will inevitably lockup after maybe 30-60mins. It doesn't BSOD, just everything freezes as it is, so the last frame is stuck on the screen and sometimes the audio gets stuck in a ms loop but tends to just go silent and I have to hard reset. When I stop CGMiner, it drops the clocks back to the default 800/1250 but MSI Afterburner has the 3D profile set to 850/1300 so it uses that when gaming. None of the overclocks change the voltage. I'm using an Accelero Xtreme III heatsink and the temps stay below 70c when mining and even lower when gaming. If I reboot after stopping CGMiner and then play a game, I never have any problems so I'm sure it's not a HW fault. Perhaps something needs resetting after mining, so I'm wondering if there's any way to do this without rebooting, as even with a SSD it's still a pain having to close everything? Anyone got any ideas what the problem might be or how to fix it?