Possible broken Mobo....

[PCNOOB]

OK from the top:

Asus M2N-E
AMD 3800 X2
2 X 512 MB Corsair
eVGA 7600GT
500 watt FSP PSU

My video card fan started rattling awhile back. I put off getting a new one for awhile. This may or may not have anything to do with my current problem, but I figure the more detail the better. One night my computer froze up, so I turned it off, and when I turned it back on, it would only stay on for a couple seconds, then power off.

I took everything out of the case and followed the directions on the sticky about this procedure, and still no dice. All fans work fine, including those of the PSU, and I even re-applied some thermal grease on my CPU, so it's not a heat issue. I swtiched out both sticks of RAM, took my video card out etc. and it still wouldn't remain powered up. Then out of sheer whimsical curiousity I unplugged the 12V 4 pin PSU plug. On the mobo this lies on the opposte side of the CPU from the RAM sockets right near the periphrial plugs. So if I unplug this plug labeled ATX 12V it turns on just fine and stays on, but I get no signal to my monitor.

What's this plug's purpose? What's most likely wrong? I'm getting no display, so could the broken VGA fan have caused a short in a pathway involving this 12V plug, which runs the video hardware? Can I try and fix this?

thanks

[flanzig1]

The 4 pin plug provides power for the CPU which is needed for the system to boot properly.
One thing, did you clean the old thermal compound off the CPU AND the CPU heatsink? If not, need to clean the old stuff off and reapply a thin layer of compound.
Your orginial problem could be due to a faulty PSU and/or mobo.

[PCNOOB]

OK, so I go to take the heatsink off and it's so adhered to the CPU from the thermal grease that it gets yanked out with it. Nice. This keeps getting better and better. Checked the CPU and no pins are bent or anything, but it couldn't have helped the matter. Does cleaning off the old compound really matter?

I cleaned off both the CPU and heatsink thoroughly (I even used a bit of acetone on the heatsink), then smeared a thin layer of compound onto the top of the CPU and clamped the heatsink back on. Still shuts off in ~3 sec. So this must have something to do with the CPU if when I unplug the CPU power everything stays on?

I built this system back March 2007.

[jdeb]

its sounds like the power supply to me but do you happen to have a spare one to try? I assume you don't, maybe you can go out and by a antec basic or cheaper just to test... or better yet borrow one. A few years ago, I went into my local Mom and Pop PC store and picked up a good 3 quality used power supply (400w, 350W, and a old dog for old dog boards) out of their used PS bin for 5.00 ea, I am still using them today on my tech bench. Never hurts to have one around even if you do not build them.

[PCNOOB]

PSU? Hmmm, that would mean that only the 12V 4 pin plug is broken and causing the computer to shut off...again, when I unplug the 4 pin 12V things stay on normally (of course there's no boot-up because there's no CPU power, but fans, HDD, and everything all stay on as long as the 12V 4 pin CPU plug isn't in)

I think my buddy's got an old PSU I can use. I'll go over and get it I guess.

[jdeb]

Originally Posted by PCNOOB PSU? Hmmm, that would mean that only the 12V 4 pin plug is broken and causing the computer to shut off...again, when I unplug the 4 pin 12V things stay on normally (of course there's no boot-up because there's no CPU power, but fans, HDD, and everything all stay on as long as the 12V 4 pin CPU plug isn't in) I think my buddy's got an old PSU I can use. I'll go over and get it I guess.

that would narrow it down, better than a spare motherboard right? wouldn't hurt to grab a video card while your at it