power cycling head scratcher

okay hope i don't get too wordy describing this but want to be sure it makes sense. 2 days ago i turned on/enabled hibernate. i shut down the pc by holding shift and clicking on standby. machine shut down fine. that night i started it up; it started up like normal coming out of hibernate just fine. i used the pc for a while then decided to shut it down. i brought up the shut down options and reached for the shift then clicked the standby to put it into hibernate. as i clicked i looked down and realized i had held down the control key. the pc shut down in what seamed a normal way but i restarted the pc and waited till it got to to the logon screen.then did a normal power off shutdown. then went to bed got up in the morning went to work. when i got home i walked into the room where the pc is and noticed it was running. before i could take 3 steps it powered off. took 2 more steps it powered back on then off in less then 10 seconds. after 10 min fighting to get it to ither fnnish booting or stop cycling i puled the power cord waited 1 or 2 and plugged it back in and it started doing it again. so it sits waiting with power supply turned off by the switch. now i am not certified but have been working on pc's since 88 this is one that i cant figure out and dont make sense i have tried every thing i could think of other then resetting the cmos which is what i am going to try tomorrow. any suggestions are welcome i have a feeling mother board went but am hoping it didn't. thanks for any time or suggestions

Hi Dragon. Definitely sounds like a hardware issue. Probably power supply (likely) or motherboard as you suggest.

well i removed the battery to reset the cmos as that is how it had to be done on this pc's mother board and after it restarted and shut down 2 more times and about 20 presses on the power on button it started took 4 trys to get the cmos to hold its settings but has been running for 4 hours now and off and on 4 times since then so i have no clue what happened other then not virus. ant complaining. thanks to anyone that thought about what was going on. have decided that is time to replace the system just have to decided what i want. i prefer to build my own but might get lazy and just buy one since i havent been messing with my setups much for last cpl years. again thanks