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Desktop PC won't POST or Start- Troubleshooting Help?

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November 25, 2010 1:25:13 PM

My home built desktop PC won’t start up. I can’t get it to enter BIOS or post. The system is about 2 yrs. Old. For the past month or two it would sporadically lose time / date settings, so I thought it might be related to a dead CMOS battery. Changed the battery and followed steps for clearing CMOS, still nothing. Here’s what I have:

Asus M2A- VM Mobo
AMD Athlon 64 X2 5000+ 2.6 GHZ CPU (black ed.), never overclocked
2 x 2GB Crucial PC 6400 DDR2 RAM
Antec Case w/ Antec Earthwatts (80 Plus) EA-500, 500 Watt PSU
eVGA geForce 8600 Nvidia video card

The mobo displays a green LED when connected to the PSU. When the power button is turned on no other lights or beeps come from the mobo. Case fans, CPU fan, Hard drive, and DVD drive all spin up. Previously I would get a beep from the system speaker as BIOS loaded.

Tried to power up w/ drives disconnected, removed RAM, and tried w/ each stick of RAM individually, removed video card, still nothing from the mobo (sound or video) when power is turned on. Called ASUS tech support, guy I talked w/ there thought it might be the mobo, waiting to hear back from them for an RMA as my mobo is still under warranty.

I ordered an identical M2A-VM via eBay (arrived in new OEM packaging) thinking it would solve my problem. Connected the board w/ same results – nothing on power up. I did clear CMOS and install a fresh battery before powering up the new mobo.

Any thoughts on if I may have a bad PSU or CPU? Anything else that would worth looking into that could keep 2 different mobos from posting and entering BIOS?

I may take it to a shop at this point for more thorough diagnostics. I’ve got an OEM version of Windows XP Media Center and don’t want to lose the license just yet. My wife will complain about having to use a different UI w/ Win 7, not ready to go there just yet.
November 25, 2010 2:27:29 PM

Your description of the situation suggests to me that the next step is a power supply test. It sounds like you've given this an awful lot of time already. Procure a power supply tester and test your power supply, or swap your current PSU for a different one. Report back on your results.

Good luck!
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a c 122 B Homebuilt system
November 26, 2010 3:47:05 AM

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 beeps 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. You do have a case speaker installed, right? If not, you really, really need one. If your case or motherboard didn't come with a system speaker, you can buy one here:
http://www.cwc-group.com/casp.html

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.

Motherboard LED's mean very little. When on, all they are telling you is that the computer os plugged into a live power socket and the PSU is switched.

Remember, at this time, you do not have a graphics card installed so the load on your PSU will be reduced.

If no beeps:
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. 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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November 27, 2010 6:20:23 AM

Thanks for the suggestions. Bad PSU. Didn't go through the entire checklist, though I've bookmarked it for future reference. It is very thorough and detailed. I'll have to get a hold of a multimeter. I was out running a few errands and had already decided to try a new PSU before checking back in to the responses I'd received.

Connected the new PSU (a cheapo from Best Buy, to be replaced by a better one). Hit the power button fans spun up then a single beep (just like usual) then into the display and BIOS. Installed the CPU and RAM on my original mobo, and same result. Typing this reply on the functional-again desktop.

I'll definitely go through the checklist if I get into this kind of scenario again. Haven't spent much $$, but have lost a few hours trying to figure this one out. Could've saved some time w/ the checklist, a multi-meter, and a paper clip.

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