Sorry about the lapse. I've also been having some automotive woes that I had to address...
Do the DMM diode check on the mobo and see.
CPU installed: Reading settled to 0V instantly.
CPU removed: Reading rose to about 0.44V over a couple seconds.
(For comparison, doing the same test on the 12 pins of the 24-pin connector, the DMM reading quickly settled to about 0.503V.)
Try testing with no CPU & RAM or cards installed. Then just RAM. Then add CPU.
The only thing that affected the results was whether or not the 8-pin CPU plug was connected or not.
If the 8-pin plug was connected, the computer had the same behavior as I described previously (CPU LED flashes, fans twitch, then nothing).
If the 8-pin plug was removed, the PSU comes to life, fans spin up, and the CPU LED remains permanently illuminated.
This was the behavior regardless of whether there was no CPU or RAM, just RAM, or both CPU and RAM.
The only other things installed for the above tests were the CPU heatsink fan, the power switch, and the PC speaker.
I was disappointed that I didn't get any beep codes for any of the above tests. Have some MoBo companies been doing away with system speaker error code output?
It seems that there's definitely an issue with the MB. Agree?
One nagging question in my mind: How likely is it that the MB took the CPU with it as it went down?