Has anyone experienced this problem? Does anyone have a solution? I have scoured the internets for solutions and found many different answers. I am on a Macbook Pro 6,1. The one that has worked for me is reset the SMC, switched to the integrated card using gfxCardStatus, not plugging in an external monitor and jacking up my fan speed to 6k RPMs. This has made my machine usable and has only shutdown 2x in the past 3 days. Anyone else have any insight? Solutions?
It sounds like your motherboard has suffered heat damage. The most likely culprit is doing something 3D graphics intensive, because the graphics chip can get a lot hotter than the CPU but the fan speed is controlled by the CPU temperature. Another possible cause of overheating is running Windows in BootCamp.
I've had that happen on a couple of different Macbook Pros (earlier models) and once it reaches this state you need a new motherboard. In my case, they were still under AppleCare so it was free. Since then I've always made sure to crank up the fan speeds before doing anything 3D intensive, and I installed fan controllers on the Windows side.
Perhaps open Console, select all messages, go to the search field and type 'shutdown' (no quotes needed) and the PRAM should have logged a shutdown cause error code the next time you boot after the power off. Please post the output here. Thanks.