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PC Suddenly Won't POST

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October 29, 2010 7:10:18 AM

I built an AMD hexacore system about a month back and all has been well. I was listening to music on it today and it went to sleep. Ok, cool I'm ready to turn it back on and bam, not even a post, let alone a boot. I troubleshot it for about 3 hours and got it to post with only a stick of ram, my spare vid card, and no HDDs connected. In this configuration I tested all 4 sticks of ram with positive results. I put in my old vid card with 1 stick, got a post. So I put all 4 DIMMs in with my regular vid card and got a post. Excitedly I started to reconfigure the BIOS (of course having to have cleared CMOS during the troubleshooting) and shut down to reconnect the HDDs (the only components not connected). I unplugged the PSU, connected the SATAs and powered her up... No post >: (
I have an ASUS mobo so I checked all of the POST LEDs and the CPU led remained lit. This entire experience is odd because it has been working flawlessly for a month. Also, I got a post once, but not again. Not sure sure what to make of all this. Any insight would be wonderful.

Oh, and because I'm out a computer, I'm posting this thread from my iPhone lol. Thanks again.

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a b B Homebuilt system
October 29, 2010 7:38:48 AM

Run this checklist, don't skip any steps. If you still are having trouble let us know.
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a c 122 B Homebuilt system
October 29, 2010 1:45:19 PM

Work through our standard checklist and troubleshooting thread:
http://www.tomshardware.com/forum/261145-31-read-postin...
I mean work through, not just read over it. We spent a lot of time on this. It should find most of the problems.

If not, continue.

I have tested the following beep patterns on Gigabyte, eVGA, and ECS motherboards. Other BIOS' may be different.

Breadboard - that will help isolate any kind of case problem you might have.
http://www.tomshardware.com/forum/262730-31-breadboardi...

Breadboard with just motherboard, CPU & HSF, case speaker, and PSU.

Make sure you plug the CPU power cable in. The system will not boot without it.

I always breadboard a new build. It takes only a few minutes, and you know you are putting good parts in the case.

You can turn on the PC by momentarily shorting the two pins that the case power switch goes to. You should hear a series of long, single beeps indicating memory problems. Silence indicates a problem with (in most likely order) the PSU, motherboard, or CPU. Remember, at this time, you do not have a graphics card installed so the load on your PSU will be reduced.

If no beeps:
Running fans and drives and motherboard LED's do not necessarily indicate a good PSU. In the absence of a single short beep, they also do not indicate that the system is booting.

At this point, you can sort of check the PSU. Try to borrow a known good PSU of around 550 - 600 watts. That will power just about any system with a single GPU. If you cannot do that, use a DMM to measure the voltages. Measure between the colored wires and either chassis ground or the black wires. Yellow wires should be 12 volts. Red wires: +5 volts, orange wires: +3.3 volts, blue wire : -12 volts, violet wire: 5 volts always on. Tolerances are +/- 5% except for the -12 volts which is +/- 10%.

The gray wire is really important. It should go from 0 to +5 volts when you turn the PSU on with the case switch. CPU needs this signal to boot.

You can turn on the PSU by completely disconnecting the PSU and using a paperclip or jumper wire to short the green wire to one of the neighboring black wires.
http://www.youtube.com/watch?v=5FWXgQSokF4&feature=yout...

This checks the PSU under no load conditions, so it is not completely reliable. But if it can not pass this, it is dead. Then repeat the checks with the PSU plugged into the computer to put a load on the PSU.

If the system beeps:
If it looks like the PSU is good, install a memory stick. Boot. Beep pattern should change to one long and several short beeps indicating a missing graphics card.

This will be a little different if you have integrated graphics.

Silence or long single beeps indicate a problem with the memory.

Insert the video card and connect any necessary PCIe power connectors. Boot. At this point, the system should POST successfully (a single short beep). Notice that you do not need keyboard, mouse, monitor, or drives to successfully POST.

Now start connecting the rest of the devices starting with the monitor, then keyboard and mouse, then the rest of the devices, testing after each step. It's possible that you can pass the POST with a defective video card. The POST routines can only check the video interface. It cannot check the internal parts of the video card.
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October 29, 2010 11:04:01 PM

I've been working through the checklist but please note, this isn't my first build, nor is it a "new" build. The computer has been running flawlessly for a month. So I'll go through the entire list, but I'm throwing that out there in case that alters anyone's advise.
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October 30, 2010 1:15:20 AM

After running a breadboard test with only the cpu, heatsink, and ram connected with of course the front panel, mobo power, and cpu power, there are no beeps, but the CPU led light still illuminates. Based on the manual, this indicates there is something wrong with the CPU. The temps have been outstanding in the CPU with my H70 water cooler, I couldn't imagine what went wrong unless it's just a bad CPU?
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October 30, 2010 10:03:33 PM

Best answer selected by pathscience.
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November 11, 2010 4:01:06 AM

I selected this answer as best not because it solved my particular problem but because I liked the PSU trick. It turns out it was my mobo that was at fault, the CPU was just the fall guy. I RMA'd the CPU and they got the same results I did, so they sent me a new one. I plugged it in and bam, same results: cpu led stays lit and the breadboarded system with no ram voices no beeps. But I'm now concerned about my cpu after plugging it in to the faulty board. I think the mobo shorted the first CPU and now I'm worried about the new one. It was only plugged in for maybe 5 minutes and 3 attempted power ups, but is that enough to possibly cause a short? I don't have a spare mobo or cpu to test either so I'm kind of dead in the water atm.
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