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Mobo-CPU fried? Not booting with 12v 4-pin plugged in.

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July 8, 2009 8:38:23 PM

Hey all, I'm having a problem with my custom built machine and I'm stumped.
A short version of what's happening: I'm not getting any power when the 12v 4 pin ATX plug is plugged in. Boots when it's unplugged.

I'm about ready to RMA a part or two, but I wanted to try to get some insight before possibly being without the wrong part for a while.

Specs first: (all stock speeds)
Core2duo E6750
AC Freezer 7 Pro cooler
Gigabyte P35-DS3L rev. 2.0
EVGA 8800GToc w/ ZF1000 cooler
4x1gb Corsair XMS2 DDR2 3200
WD raptor 150g HDD
Seagate 500g HDD
Corsair VX550 PSU
Antec900 case
Creative X-fi Fatal1ty
Vista 32bit
System built 11/07

So here's my issue. It's been running fine forever, but a few weeks ago I broke one of the 4 plastic tabs off the CPU heatsink. It was still seated securely and ran fine for a few days (except 5 degrees warmer, still under 45C), then I replaced the broken pin, applied a thin coat of arctic silver, and reseated the heatsink. This is when my problems began...

Now it wouldn't boot at all. When i hit the power button, fans would spin and everything would light up for 1/2 second, then shut off. I tried reapplying the thermal grease and reseating, but no luck.
I pulled everything out of the case for a barebones bench test, and still the same results. I eventually figured out that if I unplug the 4-pin 12v connector, it would boot! But obviously no video output. I've tried clearing the CMOS, and I've tried every combination of hardware, pulled all the RAM, tried just 1 stick, and still the same. I tried a different power supply (Ultra 500w X-connect) with the same results.

I removed the CPU and heatsink, and it boots with the 4-pin plugged in! But once I reinstall the CPU and cooler, it turns off right away again.

The board doesn't have a speaker, so I threw one in from an old board, but I don't get any bios beeps whatsoever.

So, I'm trying to figure out if it's the CPU or MOBO that's fried before I send one back.

I'm also now getting "No signal" from the video card whatsoever, so that leads me to believe it's a mobo problem. Would a bad CPU cause no video signal?

I am about to send the Corsair PSU in for RMA as well, since recently it's been shutting off on me randomly. I wonder if this has anything to do with my current issue?
EDIT: When it started shutting off on me, I replaced the PSU with the Ultra X-connect 500w which ran fine for a few weeks before the issue happened with the 12v plug.

I'm not impressed with what I've been hearing about Gigabyte's RMA process, and don't feel like waiting 5 weeks for them to return it :( 

Sorry for the lengthy post, but there's my issue. Does anyone have any insight whether it's the CPU or motherboard?

BTW, I found this thread that sounds like my problem almost exactly. http://forum.corsair.com/v3/showthread.php?t=78804
Maybe the PSU fried the board?

Thanks for reading, and thanks in advance for any help!

Gregg
July 8, 2009 9:12:45 PM

To me it sounds more like a PSU problem. I don't think you fried your CPU if it was able to work under acceptable temps when the plastic tab broke then there is really no reason for it to fry on you.

However since you tried a different PSU and got the same results this leads me to believe your motherboard may have damaged by the unstable PSU. Never ever use a PSU that you know to be faulty.

I'm not trying to sound like a jerk when saying this but you should feel lucky that Gigabyte will RMA it at all. The problem was caused by the PSU not the motherboard so its not Gigabyte's fault in anyway. In fact I wouldn't even put the blame fully on the PSU either as you continued to use it when knowing it was faulty.
5 weeks to get a new free motherboard that fried because of your negligence is nothing to whine about.

I also advise you to find out if your CPU has been damaged as well. It could have been damaged with the motherboard. Hopefully that's not the case but its best to know before you wait 5 weeks if you need a new CPU as well.
July 8, 2009 10:28:10 PM

Thanks for the quick response. Though you reminded me of something I left out in the original post. As soon as I started having the issues of it shutting off, I pulled the corsair psu and was running the ultra PSU instead. It ran fine for a few weeks without shutting off, until I tried to reseat the heatsink. I understand your comment about negligence, I unfortunately forgot about this part of my process while typing the original post.
I'm seriously considering buying a spare cheap mobo for now since I use my computer for some work and can't go long without it. I'd just hate to buy one and find out it wasn't the problem part. I've checked with local friends and unfortunately nobody has a spare mobo or 775 processor to test with :( 
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July 9, 2009 1:04:50 AM

The 4 pin connector supplies power to the graphics card which is why you don't get any video output, try replacing the graphics card with the 4 pin connector pluged in.
September 20, 2011 9:14:00 AM

If possible, please let me know how it worked out as a friend of mine is having a similar issue with his ASUS mobo.

Thanks.
!