As always, it could be many different things but...
1. Maybe it is the motherboard battery? Try replacing it?
2. I would try resetting the motherboard. There would be either two or three metal pins sticking out where you can short them, then replace it how it was before and try it again. This is usually called the CMOS reset pins/jumper. The jumper is the small black plastic with metal inside piece you use to short the pins to reset the motherboard.
3. Ram or CPU went dead? I don't know if you consider those peripherals.
I tried to be as descriptive as I could for other users looking up answers to a similar problem. Best of luck. Let us know how it goes.
System has been running for a couple of years but now when I try to power it on, nothing happens. If I unplug it for a few seconds, then plug it back in and start it, the power let comes on for a second, the fans (CPU, Power supply and external case fans) start to spin but stop alomst immediately.
This is an ECS (Elite Systems) Motherboard with a Celeron 600 processor. Have tried disconnecting all peripherals, and no change. Different power supplies don't even give the 1 second of "up time."