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OS not loading / random power off - Hardware fault?

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March 7, 2010 10:16:04 PM

I'm troubleshooting a computer for a family member, and I'm at a bit of a loss as to the source of the problem.

The computer will (usually) post, and then start to load windows, but generally powers off before reaching the login screen. At times, the computer will not even post, spinning up the fans for about three seconds before just dying. I have successfully run the Inquisitor livecd for testing purposes, nothing came back at fault. I did have to use the failsafe mode, running the standard mode resulted in the same aforementioned problem of the OS partially loading and then the system powering down.

I tried popping in a spare SATA drive and installing Windows fresh, same issue. The system powers off during the "Windows is loading" screen.

The motherboard is an Asus P5LD2, the processor a Pentium D at 3Ghz, if I remember correctly.

One pass of memtest86 came back clean.

Using an external PSU checker, all voltages looked good.

After one of these hard shutoffs, I must turn off the PSU or unplug it and replug it (from wall) to get it to power back up.

This is leading me to suspect a faulty PSU, however it makes me nervous that I'm able to run some software, such as memtext86 or the failsafe mode of Inquisitor, but I can't load into Windows.

I do not have access to a spare PSU to test with, so at the least I will be shelling out 35-40 dollars just to test that, if not to replace it. If that is not the issue, I am suspecting the motherboard.

I have not yet checked the caps in the mobo to see if any of them have gone bad.

PSU is an Antec SMARTPOWER 450 watt, has the thermometer-controlled fan.

There's an Nvidia GPU in here, I haven't yet taken off the vent ductwork to take a further look at this.

It is my understanding that this has been a recurring problem that has gotten worse over time, over about a year I believe.

I'm hoping to isolate the problem part prior to having to make any replacement purchases. Any ideas as to what the culprit might be?
March 7, 2010 11:37:28 PM

Try checking the voltage and /or replacing the bios back up battery
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March 7, 2010 11:46:22 PM

Checked the voltages of the PSU with a PSU tester, everything was well within tolerances.

Haven't tried replacing the BIOS battery. Certainly the cheapest part to replace. I'll try that and report back.

UPDATE: Tried replacing the BIOS battery (Had one in a junk drawer!) and no change. First power-on, the computer shut down just after the BIOS beep. Second time through, after powering off the PSU by the switch for five seconds, it booted up and let me configure the bios. I tried to go into Windows, and it shut down before the Welcome screen loaded.
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March 15, 2010 7:59:28 PM

This turned out to be the power supply. I ordered a $40 supply on a whim to see if it fixed it, and the computer has had no problems since.
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