Motherboard won't boot!

[MegaBlaze007]

Well...one more strange problem with my PC! As the title says, my motherboard won't boot up but randomly boots up by itself!

Now a detailed explanation.
Firstly my motherboard is Asus P5GC-MX/1333. When I first got it, I had a 20-pin PSU of 300W and I've used it for about 2 weeks. Then one day, when I came home I wanted to use my PC as always but this time it wouldn't boot up! I didn't know what to do, I opened my CPU and started staring at it, hoping to find a solution when suddenly, the motherboard boots up all by itself! It didn't load the BIOS though and it wouldn't even turn off so I had to turn off the power switch directly. Then I turned on the main switch and tried booting up the board again but it wouldn't boot up once again and after a while booted up by itself(BIOS not loaded once again). After a number of tries it finally booted up and loaded the BIOS normally and I was able to use the PC.

As the PC finally booted up normally, I took the chance to read the manual of the board in which I found that if a 20-pin PSU is used, a minimum of 350W is recommended! So the next day I bought a 20+4PIN PSU off 500W and connected everything. Back then, everything was working normally, motherboard booting up with BIOS loaded. The following day, I faced the same problem again and even today, before I could come on tom's hardware I faced the problem!

Now one thing is clear, the problem is not about the PSU cause its new and I feel is delivering enough power to the motherboard. Is it the motherboard, ram or something else?

 

[o1die]

That board is near the end of life as far as the capacitors go; or it could be a short somewhere. I would remove the board and check for a loose standoff or loose wire underneath. Check the backplate for metal to metal contact with the ports on the board. Last I would reset the bios by removing the board battery in case one of the power on settings is wrong, such as set to boot by the keyboard or mouse.

 

[MegaBlaze007]

That board is near the end of life as far as the capacitors go; or it could be a short somewhere. I would remove the board and check for a loose standoff or loose wire underneath. Check the backplate for metal to metal contact with the ports on the board. Last I would reset the bios by removing the board battery in case one of the power on settings is wrong, such as set to boot by the keyboard or mouse.

i tried only one of those you mentioned...removed the battery to reset bios...can you please explain how to do the others please?

 

[o1die]

The other recommendation is simply to remount the board inside the case; while it's off, check under and behind the board (backplate) for any loose wires, standoffs (under the board). You're checking for any contact that could cause a short. It's a longshot, but at this point, if you want the problem to stop, it can't hurt. Bad capacitors are something that most folks won't try to replace; the parts are cheap enough, but soldering them into the board is a little tricky, not for amateurs.

 

[MegaBlaze007]

The other recommendation is simply to remount the board inside the case; while it's off, check under and behind the board (backplate) for any loose wires, standoffs (under the board). You're checking for any contact that could cause a short. It's a longshot, but at this point, if you want the problem to stop, it can't hurt. Bad capacitors are something that most folks won't try to replace; the parts are cheap enough, but soldering them into the board is a little tricky, not for amateurs.

i checked everything...no loose wires or contact with backplate, i even tried booting the board in my hands! yet nothing...today i observed something..i let the main switch on...and after about 15-20 minutes i tried booting the board and it started...without the bios though! so i had to turn on and off until the bios is loaded. it's some kind of warming up before the board is booted properly!