Bf2 crashes the whole pc

[timebomb17]

guys when I play Project Reality, after about 40 minutes playing my pc crashes, LOCK IT!, stop listening and who is on skype and mumble or control + alt + del works, just resetting it, and it only happens in reality project, in other games even heavier does not happen: /
my configs:
Core 2 Duo 2.2GHz
4gb ram
EVGA GTX 460 1GB DDR5
win7 64bit