PC not booting, mobo or CPU?

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travbrad

[H]ard|Gawd
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Jan 11, 2005
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I got a new SSD in the mail today so I decided to clean out my PC while I was installing it. I also decided to re-apply thermal paste to my CPU while I was at it, and clean the dust out of my video card. After putting everything back together my PC no longer boots for some reason. The HSF and case fans spin up, but I get no POST and nothing shows up on the monitor.

At first I thought it might be a video card problem, but I tried a different video card in my PC and that didn't work either. Then I thought maybe there was a problem with the PSU, but I plugged my PSU in to my brother's mobo and it worked fine. Plugging his PSU in to my mobo gave me the same result as before (all the fans spin up but no POST or monitor display). I also tried swapping RAM just to be sure and that wasn't the problem either. I've also tried resetting the CMOS jumper, and even removing the battery for awhile.

So it seems to be an issue with either the motherboard or CPU. Is there any way to be sure which one it is before I go buy a new one tomorrow? Unfortunately I don't have a spare Sandy Bridge CPU or 1155 mobo to swap out and test.

I am leaning towards it being a motherboard problem right now but I'm not completely sure. It seems unlikely that I would have bent a pin while re-applying thermal paste since the pins for SB are on the motherboard socket, not the CPU itself. I double-checked the CPU as well to see if I somehow got thermal paste on something other than the heat-spreader, but I don't see anything.

Thanks for any [H]elp you can provide.
 
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Try a barebones bench test: Take the motherboard out of the case, place it on some cardboard (ideally, the motherboard box), and try booting the system with just the board and processor.

You should also replace the CMOS battery (and reset the CMOS thereafter) as an insurance measure. The CMOS battery is a simple CR2032 watch battery.
 
I tried the barebones bench test and I still get no beeps even with everything but the CPU removed. The HSF is still spinning up, but that's it. I'll try to get a new battery tomorrow when the stores open, it's 2AM right now. If I get no beeps no matter what I do couldn't that still be either the motherboard or CPU?

One other note, my little PC speaker is definitely working too, I tested in on another PC and heard the normal single short beep.
 
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Since power is still going through everything, I believe (but can't confirm) that the processor may be bad.
 
If you had pulled the cpu out of it's socket when you cleaned the old thermal off, I would recommend pulling it out again and check the bottom of the cpu for left over thermal grease. Also check the motherboard socket for any bent pins. All the pins should line up cleanly. And check that no left over thermal has fallen in the socket.

If all that is clear/clean then check the memory slots and card slots for left over dust or debris.

For me if that all checks out fine. The it could be either cpu or motherboard. To test those I would have to try swapping the cpu with another system.
 
Thanks for the replies everyone. It turned out to be a failed motherboard. I'm not exactly sure what failed or how, but I ran to Microcenter this morning and picked up a new motherboard (figured I'd start with the cheaper of the 2 potential bad parts) and everything is working perfectly now.

This SSD is blazing fast. I should have gotten one sooner. The bios splash screen lasts longer than windows boot does I think :)
 
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