Troubleshooting help for my Sager NP8651

I bought the Sager NP8651 in June 2015, and have loved it until now. About 6 weeks ago, it started giving the "beeping" sound often associated with overheating, and would auto-shut down after ~30 seconds. It would only do it when I was playing video games. I bought a new cooling pad, and while it would still ocasionally beep and shut down, it did it far less frequently. I thought the problem was "solved."

Then this morning it beeped and shut down (like before). Only this time, it's...

Troubleshooting help for my Sager NP8651