Computer won't POST

[thecraichead]

Hi guys,

I'm trying to diagnose the fault in my PC following a sudden power off. Ever since then the computer will power on for only a couple of seconds before turning itself off. The fans and hard drive spin but there are no beeps or POST screen. The monitor does not activate on power up.

Specs are as follows:

Asus M2n32 sli deluxe
AMD athlon 64 X2
Be Quiet! 500W PSU

I have done much troubleshooting, ruling out any shorting from the case, reset the cmos, took everything out and the same symptoms persist with only the PSU and CPU fan plugged into the mobo, with all out on a desk. PSU is plugged in properly, with 24 pins and 12V molex attached. Took all RAM out hoping to hear beeps, no joy!

I am wondering if it is the motherboard? It is only about 1.5 years old so I would expect it to last a bit longer. The only strange behaviour before this was that some of the USB ports did not work recently. These were auxillary ones so I presumed that they may not be plugged in properly inside. However, when I opened the case they were secured properly.

Anyway, any ideas how I can troubleshoot further or what the problem may be? There is no visual damage to the mobo by the way..

Thanks all..

 

[montyuk]

sounds like its kicked the bucket. whats the asus warranty like?

 

[unclefester]

I know this is a dumb question, but when you reset the CMOS did you pull the on board battery?

 

[thecraichead]

hey guys,

yea I pulled the battery and changed the jumper.. I suppose it must be the motherboard eh? I don't think I have the receipts anymore so no warranty probably. Would you say I should bite the bullet and buy a new one. The only thing concerning is that there is a small chance it may be the PSU

 

[boonality]

I would start with power supply because it's the easiest to swap with a buddies and test. Also I would say that it most likely is your power supply. Motherboards will at least "complain" if they are broke.

 

[thecraichead]

Just about the PSU, I tried mine in an old Dell, and that PC beeped and Posted.

I tried the Dell 350 W PSU in mine, and nothing happened except the usual described above. Led was on, fans came on the all shut off before Posting.

Does this tell us that it is not the PSU?

Thanks for the help guys

 

[boonality]

Well it's likely that your PSU is ok, try this first though before you go out and buy another mobo.

Pull out your video card and try to post and see if the results are the same, then pull your hard drive as well. What you are trying to do is elicit a response that your motherboard is at least getting to a specific point but unable to complete post.

If you just so happen to have access to another motherboard you could always swap, but the above quick tests will tell you that if your motherboard behaves the same after you remove the video card and hard drive, then yes it's your motherboard. It should yell at you saying that the component is missing if it's at least getting that far in the post.

 

[thecraichead]

yea, its all out on the desk, only case power button and PSU and CPU fan are plugged into it. Won't post..

I might try sprinkling some holy water on it while pressing the power button repeatedly

 

[jsc]

With just the PSU, CPU, and motherboard connected, the BIOS should detect a memory failure - generally long single beeps. Silence indicates that one or more of the three are bad.

"Led was on, fans came on the all shut off before Posting.
Does this tell us that it is not the PSU? "

No. The LED on the motherboard is powered by a small, always on, separate Standby Power Supply. In addition to the main 5, 12, and 3.3 volt outputs, the PSU also sends a control signal called something like "PowerOK" (grey wire, pin 8). The CPU needs this signal to boot.

What could be happening is:

You press the power button.
The PSU starts generating the main power outputs.
After they are up and stable, the PSU sends the "PowerOK" signal to the motherboard and CPU. This should take 200 - 300 msecs.
The CPU sees this and starts to boot and run the POST.

At this point, if any of the main outputs drop out of tolerance, the PowerOK signal goes low (5 volts to 0 volts). This forces a CPU reset and shuts down the PSU.

The fault could be in any of the three components - in order of likelyhood: PSU, motherboard, CPU.

 

[thecraichead]

thanks for the help man, that is useful info.

do you think that the fact that my PSU caused another computer to post and beep suggests that it is working ok?

I have no other computer to test in really. I have to try and identify the faulty part. Any suggestions how?

 

[jsc]

"do you think that the fact that my PSU caused another computer to post and beep suggests that it is working ok? "

Not necessarily. If the other PC did not put as much of a load on your PSU, it could still work there burt not with your original PC.

"I have no other computer to test in really. I have to try and identify the faulty part. Any suggestions how?"

Unfortunately, once you are down to PSU, CPU, and motherboard; you are limited to testing by substitution.