Working Sierra install stuck in endless reboot after 2 month shutdown

[toddo]

Hello everyone,

I just returned from a two month trip overseas. Before I left I unplugged the surge protector/computer just to be double sure nothing happened while I was away. I live in the Philippines, not the best electrical grid in the world. When i returned today, I plugged the surge protector back in and tried to power the system up. It powers on, no signal gets to monitor and then reboots after about 2 seconds. I can't get anywhere to figure out what the problem may be. My system was fully functional for years before I left for vacation. Any suggestions would be most appreciated.

 

[BreBo]

Any suggestions would be most appreciated.

Maybe CMOS battery fail.

 

[toddo]

Thank you for the suggestion. I replaced the CR2032 battery with a new one, but same problem. Press power button, fans kick on, one beep, then within 3 seconds reboot and repeat. Also tried holding Command+Alt+P+R, pressing power while holding down either shift or C keys, nothing so far gets past the 3 second mark.

 

[P1LGRIM]

Also tried holding Command+Alt+P+R, pressing power while holding down either shift or C keys

That is for Macs, no expectation of it having any effect on a PC.

You could try :
Disconnect the mains power lead.
Press and hold the "On" button for 30 seconds, then release.
Reconnect power.
Switch on and test.

Other than that, reduce to minimum configuration - Just CPU, memory and graphics - Disconnect everything else.

 

[toddo]

Hello Pilgrim. Thank you also for your suggestions. Tried disconnecting main power and 30 second test first with no result. Then per your suggestion, disconnected everything to minimum config. and still have same issue. Power on, fans spin up, one beep, then power down and reboot, whole process takes approximately 3 seconds. 2-3 second pause then repeat.

 

[P1LGRIM]

Power on, fans spin up, one beep, then power down and reboot, whole process takes approximately 3 seconds. 2-3 second pause then repeat.

Switch to backup BIOS if possible, otherwise something is terminally damaged.

 

[toddo]

Switched to backup BIOS, same problem. Do you think failed motherboard?