Hey guys so I recently installed a q8400 cpu into my machine, however the intel heatsink shipped didn't want to go in so I've put in the heatsink old e5500 that came with the computer (dell inspiron 560 - commence barrage). I am now often getting event 41- kernel power, in which the computer just instantly powers down then restarts often, while doing menial tasks like word processing and web browsing. I sometimes have 4-hour long binges of games, especially the cpu heavy bad company 2, with absolutely no issues. I have run prime95 for an hour without any failures, although i could run it for longer if you think it would help. At 100% load the max the cores were getting to was 70C, which seems a bit high if you ask me, but the only time the restarts are occuring are at a lot less than this.
Swapped out old psu and vid card a while (3 months) ago, and issues only started with this cpu.
intel q8400 (with old dell heatsink)
Dell mobo (0k83v0, not that that should mean anything, latest bios installed)
6GB DDR3 ("nanya technology" aka whatever dell chucked in there)
powercolor radeon hd 5770
ion 2 vantec 620W PSU
Windows 7 home premium