Power Supply or motherboard

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Wolfie2U

n00b
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Aug 24, 2010
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I'm having an issue with my computer and I'm trying to determine if it is the power supply or motherboard. The power supply is a PC Power & Cooling Silencer 750. The motherboard is an Asus P6T/1366. The computer is totally powering off as if I've pushed the power switch. This behavior happens at any stage of the boot process and when in Windows 7. When it shuts off, all fans, drives and activity are gone. Strangely, both the power and reset switch on the motherboard stay illuminated. However, the only way to restart is to turn the switch at the power supply or disconnet the supply from the wall outlet. I was in the BIOS under the power menu and the 5V voltage was fluctuating madly from 4.8V to 5.8V (it shut down shortly thereafter). The motherboard had been slightly overclocked (3.5) but I reset the CMOS and it is running at default settings with the same results. Heat before and after resetting the CMOS was around 50C. When it is running, there are not apparent issues until the shutdown. I've had this system running since December 2008 without issues. Any ideas?:confused:
 
It is likely your PSU is starting to go bad, but that cannot be confirmed based on what you're saying. If the 5v line is fluctuating a lot, get out a multimeter, and test the molex voltages. I believe the red wire is the 5v, but you can test both to make sure. Software voltage is fairly unreliable. If the multimeter reads the same fluctuations, then you do have a bad power supply.

I had an issue once where my computer will shut down randomly, but the motherboard power LED's would remain on, etc. What I found the issue to be was that me shorting the green and black lines on the motherboard connector caused the green connector to open up, causing poor contact with the motherboard. Any vibration would cause it to momentarily lose contact, and shut off the computer. Solved this by sticking a screwdriver in there and closing up the green connector, and I haven't had a problem since.

Your best bet at troubleshooting would be to try out a different power supply in your computer, or try your power supply in a different computer. Or both.
 
Most likely a motherboard issue, but the best course of action is to try a different PSU in that PC or that PSU in a different PC to try and isolate the issue.
 
Without a machine that tests PSUs, it is almost impossible to verify the PSU is good or bad on those rails. A voltage meter will only look at that time. The BIOS gives an estimate. I've ran into this issue once and it turned out to be the motherboard.
 
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