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Computer powers up, fans on - but will not POST

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April 2, 2011 11:55:55 AM

Hi folks,

Looking for some advice on an issue I am having with my PC. It have had it for 3years with no issues at all, but recently when I turned it on the monitor did not come on. After more investigation it seems that BIOS does not POST - i.e. I don't get my usual beep when it boots. The CD drive and hard drive and fans and power lights are all powered but it will not boot.

I have spent some time on Google and tried the following:

- Power supply: multimeter shows that 12, 5 and 3.3V supplies are spot on. Also green LED on motherboard is lit.
- RAM - tried removing this completely, still no error beeps from BIOS
- Video card, HDD, CD drive all removed - still no beeps
- Reset the BIOS to default - no change
- Case does not have a reset button but the motherboard jumper is correct (i.e. its not held in reset)
- and yes - the monitor works fine :kaola:  tested from laptop

Any ideas as to what else I could try? My gut feeling at the moment is that the motherboard is broken however I have no idea why this happened - I have literally never even opened the PC case since I purchased it. The only other thing I could think is a processor problem, but I'm sure the BIOS would still detect this - is this correct?

Spec:
Processor (CPU) Intel® Core™2 Quad Q6600 (4 X 2.40GHz) 1066MHz FSB/8MB L2 Cache
Motherboard ASUS® P5N-E SLI: Quad-core CPU Ready, NVIDIA® Dual X8 SLI
Memory (RAM) 4GB CORSAIR DDR2 667MHz - LIFETIME WARRANTY! (2x2GB)
Graphics Card 512MB GEFORCE 8800GT PCI Express + DVI + TV-OUT
Memory - 1st Hard Disk 500GB SERIAL ATA II HARD DRIVE WITH 16MB CACHE (7200rpm)

Thanks!!
a b V Motherboard
April 2, 2011 7:08:06 PM

When you removed the graphics card did you replace it with another? If I recall some motherboards will refuse to post if there is no graphics hardware.

Don't suppose you can beg, borrow or steal another 775 CPU? Idea being you could drop something else in to see if it's your Q6600.

Potentially could be thermal creep but this is wishful thinking. You've obviously reseated the RAM and the GPU but make sure the connectors are dust free. Especially if the machine hasn't beat cleaned or even opened in 3 years.
a c 156 V Motherboard
April 2, 2011 7:24:46 PM

What kind of PSU? And do you have the "PwrGood" signal from the PSU? You can have all of the power outputs from the PSU, but without this, the PC will not boot. Later in this post, I will tell you how to check it out.

Work systematically 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.
The following is an expansion of my troubleshooting tips in the breadboarding link in the "Cannot boot" thread.

I have tested the following beep patterns on Gigabyte, eVGA, and ECS motherboards. Other BIOS' may be different, but they all use a single short beep for a successful POST.

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 once you are finished.

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%. If you have a white wire (many modern PSU's do not), it should be -5 volts.

This is the PwrGood signal
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...

A way that might be easier is to use the main power plug. Working from the back of the plug where the wires come out, use a bare paperclip to short between the green wire and one of the neighboring black wires. That will do the same thing with an installed PSU. It is also an easy way to bypass a questionable case power switch.

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.

Silence, long single beeps, or series of short beeps indicate a problem with the memory. If you get short beeps verify that the memory is in the appropriate motherboard slots.

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.
At this point, if the system doesn't work, it's either the video card or an inadequate PSU. Or rarely - the motherboard's PCIe interface.

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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April 3, 2011 7:42:53 PM

Thanks for the comments. I worked my way through the check list and tried the breadboarding technique but still saw the same results.

PSU is 600W Quiet Quad Rail PSU + 120mm Case Fan. I have checked the PwrGood and it goes to +5V upon power up.

Unfortunately I don't have another CPU which I can test. My gut feel is that the m/board is the issue but I would like to rule out the CPU before I order a new M/B.

If I removed the CPU and powered up should I hear an error beep from the BIOS? I assume if I don't hear anything then the M/B is at fault.

Final thing - I have seen some comments saying I should "flash the BIOS". I assume this is not possible if you don't reach POST?
a b V Motherboard
April 4, 2011 9:27:30 PM

PerlonKid said:
If I removed the CPU and powered up should I hear an error beep from the BIOS? I assume if I don't hear anything then the M/B is at fault.

Final thing - I have seen some comments saying I should "flash the BIOS". I assume this is not possible if you don't reach POST?


I'd be amazed if it even drew power without a CPU installed so I don't think your technique will work.

You've tried removing the battery for a while to reset the bios right? I'd maybe check that the battery still has a charge as well!
April 25, 2011 10:57:31 AM

A quick update in case anyone searches for this thread in future:

Due to other commitments I didn't have the chance to work on the PC for a week. When I did, I tried a final boot and this time the BIOS reached POST and gave a continuous beep (RAM failure). I removed one of the 2GB RAMs and the PC booted correctly!

I then re-seated the RAM and it booted correctly with the full 4GB. Given that I had did this several times during debug I have no idea why it suddenly worked this time!

I guess there may be some intermittent problem with the MB and I wouldn't be surprised if it happens again in the future. The only thing I can think that may have helped was cleaning out the dust in the inside of the case with compressed air - that's the only thing that I physically changed since the issue occurred.

Thanks again for everyone's help and advice!
a b V Motherboard
April 25, 2011 11:47:11 AM

Glad you got it sorted dude. Fingers crossed it continues working!
April 25, 2011 12:45:06 PM

I had this exact problem with my ASUS P5N72-T Premium. I had to RMA the motherboard twice, then they switched me to the P5N-T Deluxe which I had to RMA twice and I'm still having problems. Glad your computer started working again with the RAM trick.
!