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computer turns on and then off 3 seconds later

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A couple days ago computer randomly turned off and since wont boot up. Now as soon as I flip the switch on the back of the PSU it turns itself on and then off 3 seconds later. There is no image and it posts nothing. I'm unable to turn it on with the power switch. The power switch wires became disconnected from the switch and I had been manually touching them to switch to power up my computer for the past several weeks. Not sure if this is related.

I've tried booting the mother board without RAM, GPU, DRIVES, the power switch, etc... plugged in and it didn't change the behavior of the computer. Although when the 4 pin ATX wasn't plugged into the computer it didn't turn itself off. The computer will only turn on if you let the green LED on the mobo turn off before turning it back on.

I assembled the computer from parts off of newegg probably 5 or so months ago. The computer had been mostly fine up until this point, although there were a few random and rare random turn offs in the past. A few weeks ago when I turned it on I vaguely recall it saying something about overlcocking failing (which I never did) and having to reset the bios for it to turn on. Also, the system time would sometimes end up set back a few hours or more. This leads me to suspect the motherboard rather than the PSU. I also tried changing the CMOS battery from an other motherboard (same model although different maker) and it changed nothing. Not sure if I changed it right, all I did was pop the other one in there.

I'm not as interested in fixing the problem as I am identifying it since I still have warranties on all the parts. Any help is greatly aprreciated.

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It might be posibility Processor over heating problem.
You need to check cooling system of your computer.
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If you want to test the motherboard and the PSu then do the following

Disconnect everything from the Motherboard except

* keyboard
* mouse
* video output
* 20+4 powercable
* 4/8 pin 12v wire both coming from the powersupply,
* Cpu fan wire
* power and reset button to the case
*case speaker

Now you should have NOTHING connected to the motherboard except what was listed above.

The goal here is just to test the mobo:

If the computer still will not boot up the please remove the motherboard from the computer along with the power supply

place the motherboard on a piece of card board larger than the motherboard,

this will eliminate a short from the mobo to the case witch could be a possibility

Install the cpu with, 1 stick ram in dimm 1, power supply, video card, case switch and case speaker
Connect ps2 mouse and keyboard along with the monitor
Repeat the above and power on

If the computer now boots into bios you most likely had a case short so make sure when installing the motherboard in the case that you use standoffs and they line up with the mounting holes in the motherboard and none of the standoffs touch anything else on the underside of the board.

Thanks to Cbarnard for these instructions
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