I am observing complete computer freeze (only reset helps) which occurs only with one application (PerfectWorld game). The game starts fine and runs correctly but then, randomly, locks the computer - between seconds and hours after starting. Outside of PerfectWorld, the computer can run perfectly fine for days and weeks and with intense graphics too. I am 99.9% certain it is a problem between PerfectWorld and nVidia drivers (if I replace nVidia card with ATI - no crashes ever occur; equally - other games never crash with nVidia). I tried all WHQL drivers from nVidia and even latest beta drivers - it makes no difference. Extensive video testing under DirectX11 shows no problems (Unigine DirectX benchmark can run for many hours). Removing hardware acceleration and reducing resolution of the game seems to make freezes more rare (maybe from twice an hour to once every 3 hours) but they never go away. Win7 compatibility - aero, DPI, XPSP2 don't have any effect on freezes. I tried also many nVidia drivers (including latest WHQL 196.21 and beta 196.34 dated 22 Jan 2010) - no luck. Is there a way to determine where the problem is - in DirectX11, nVidia drivers or PerfectWorld software? Any ideas or advice? I found a few crash dumps (much less dumps than crashes though!) and WinDbg tells me "Probably caused by : nvlddmkm.sys (nvlddmkm+7df0c)". That is the address for 196.34 beta driver (same address for 3 dumps that I found). Configuration: ABit QuadGT motherboard, Windows7 64-bit, 4GB RAM (memtested), Intel 6600 @2.4GHz (no overclocking), nVidia 9800 GTX+, Tagan 700W PSU, all temperatures OK.