I have a customer's Vaio that does that thing exactly,
In this case it is definitely not heat issue, battery, power, or hard disk. I am in the process of running some other tests off windows, such as CPU, GPU and RAM stress tests but i seriously doubt that would be the case. My suspicion is drivers, even though i have disabled the one's that haven't been installed, from other forums I saw it could be GPU drivers, so try uninstalling your GPU driver and re-installing it. As a pro I cannot go directly to that solution without checking that everything is in perfect condition, but try it and let me know :)