I had the two red rings - signaling overheating.

I tried cleaning the fans out without any effect.
Then I tried cleaning off the heatsinks and applying Arctic Silver. I also added an Evercool fan- still nothing... it would last 2-3 minutes tops.

Then I tried replacing the XClamps with screws/washers ($4 at Ace Hardware) as outlined here, and my problem has been solved.

Thanks so much.