Intel core i7 870 stock overheating

hi. i have a PC which i mainly use for music production. i sometimes game on it, but nothing too serious.
i recently crashed both my PC's by installing the ATI Catalyst Control Center v10.12. now that i have removed that, i wanted to convert a video. and that's where the problems started...
i used Handbrake, and just let it run. it ran at about 200-300 FPS, and used about 70% CPU. after about 1 minute my PC suddenly shut down.
i checked with Coretemp, and yes, when running handbrake my CPU temps suddenly skyrocket. in 1 minute they were already hugging 90*C, which i know isn't very good for your CPU lifespan.

now i wonder what could've caused this, because before my pc crashed because of that ATI driver, i also converted videos... i think. i don't really remember because i'm not on that pc all the time, but i'm still quite sure because i convert vids all the time to ipod-size.

anyway, cooling is stock, nothing OC'ed, i have checked BIOS and the fan speed is regulated. my ambient room temps are at 19*C - 22*C.

does anyone know what could've caused this? could it be a software issue? or do i just need to reseat my cooler?

thanks in advance. i'm getting tired of all these screwed up pc's -.-