off the topic of heat if cooling doesnt work for you, i have a desktop system that has similar issues as you describe, the heat may just be normal for the machine if the compound used for the heatsink is old.
I found my system to blue screen, stutter and crash unless i reset my priorities,
i know what caused this on my system, not only does your processor and gfx chips get hot but heat has a major effect on your memory banks too and if like my laptop yours are next to the cpu it could be that.
I changed my speed setting on my pc as i have a clockable board and downclocked my memory speeds to 333mhz from 400mhz that fixed my problems ! if your lucky enough to be able to try this it may fix your issues