X51 R2 Power Loss

I bought Alienware X51 R2 from Dell’s outlet 11/15/2013. It’s served admirably, but in the last few weeks it’s taken to suddenly going blank, as if the power’s been yanked.

The shut-downs seem to occur when I’m using video-heavy programs like Adobe Premiere, or running Skyrim.

Drivers are up to date. Alien Autopsy notes the shutdowns. PC Check gives a clean bill of health. The ePSA test finds no problems. I hear the fans revving unhindered when I restart, so it’s not a wire blocking the fan. The case doesn’t feel warm at all.

After the last shutdown cost me a few hours work, I went into the Bios and disabled PCIe gen 3.

That seemed to work for half the day, so I finished editing a video project. Afterwards, I went into MS Word – and about ten minutes later, got another shutdown (or rather, power loss, since there is no shutdown procedure). This time at least, the system rebooted on its own.

Past that, I don’t have any idea how to begin diagnosing this. Any help appreciated!