Uncommanded Restarts Eventually Leading to No Complete Boot
About a month ago my mid-2011 i5 Mac Mini started performing uncommanded restarts. Specs: 16gb RAM, original 500gb HDD in the primary position (thermal sensor intact), 500gb SSD in the secondary bay. At first the restart frequency was every 30 minutes to an hour. In time, the frequency increased - but I could get it to stay up for extended periods by running certain apps in the foreground.
Eventually it got to the point that the frequency of restarts were so great that it became unusable. And finally, it would not even finish booting.
In an effort to solve the issue, I:
1. replaced the fan. (it was getting noisy and obviously failing)
2. Replaced the power supply. (thinking the failing fan had over stressed and damaged it)
3. tested individual RAM sticks by inserted them, one at a time, into different banks.
4. Pulled the fan and shroud to access the drive connectors. Disconnected the SSD. No Joy.
5. Reconnected the SSD, disconnected the HDD.
Aha! It booted immediately!
Thinking I had identified the old 'original' HDD as the villain in my scenario, left it disconnected. Reinstalled the shroud, fan and bottom cover. Re-plugged my connectors, mouse and keyboard - fully expecting to be delivered from my discomfort.
Hit the power button and smiled as I watched the boot status bar scoot up to about 80%. Then... uncommanded restart! About one in six times it would finish the boot process and display the desktop, only to restart within 30 seconds.
So... I'm back to zero and my Mac Mini is a brick.