Do you have a utility that monitors the chip and motherboard temperature?
My laptop used to do that, when the chip passed 96ºC. The "fix" was to clear out the fan so that it could blow enough air over the heat sink etc.
Processor-intensive applications, on a machine that's running close to the limit, can cause that sort of problem.
I don't know about the Media Player 11 issue - I wouldn't be surprised if that isn't doing the same thing to your CPU.