Whenever I am palying the sims2 or any other demanding game requiring high-end graphics. After a couple of hours of play - of even minutes the system just resets itself and continues through post as it would after turning it on. Also when this happens the CPU ehatsink is very loud and is obviously trying to coll the cpu form a very high temp??? Thermal seal is fine and My ATI RAedon X600 (?) has a heatsink , but no fan. Thanks!