For some reasons that I can't figure out my system shut down and restart at time up to 4 time during a session, I check all of the cables to make sure they where in properly. Some time it will run for days without any problems.
My board is a DG35EC 3GH with core two duo and 4 GH of ram ruining Window 7 home premium 32 bits.
Have you recently switched to AHCI? This also controls power management. I did a change post-install using the Microsoft regedit method and am hoping everything is OK.