Its due to the too low voltage of ideal profile, try increasing them a bit, and whats the bit rate of the video ? is it a tad higher than the previous videos you've watched?. Because of increased disk activity + more work for the processor + more work for DSP for an increased amount of time, it might reboot sometimes.
you can easily edit the voltage profile for best results. always avoid presets coz every chip is not the same

cheers.
nkirk