Originally Posted by
Kiko
Problem solved.
I took out the fan and heatsink assembly one more time, and this time I noticed a small crack in the plastic heatsink mount, which caused the copper disc on the bottom of the heatsink to pull away from the CPU board. Apparently, it was still making small contact before I had removed the heatsink. But once I removed and reinstalled it, there was no contact, which is why it powered off so quickly.
I bought an all metal replacement heatsink/fan, so this problem should not happen again.
BTW, Gary, the repair shops wanted from $100 -$300 to diagnose the problem and much more for parts. I'm sure they would have also tried to sell me an unneeded CPU board as well.
By "tinkering" with it myself, it only cost me $25, and I also gained a lot of knowledge.
Thanks to all who responded.