Shutting down & re-starting on its own!

Hi all

I've had this issues for ages now and its driving me mad! I've had all the fans ect cleaned out in case it was due to overheating but the fans are all working and its still shutting down. Tends to do it more when my son is running games like Minecraft or Kodu and is showing in the event ID as 1001 BugCheck and 41 Kernel-power.

Any help, ideas or advice would be great, thanks all