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After I had shut down my computer and unplugged it to clean my desk I hooked everything back up to find that it would not turn on. The PSU, fans, or lights do nothing when I hit the power button. The green power light on the motherboard is on and devices with lights turn on with the computer off as well.

I know it is not the PSU because when plugged into my brothers computer it will start.

Have tried: Resting CMOS Changing plugs checking all cords, and re checking all cords WAS not even bumped when I moved it Removing GFX cards No damage can be seen on motherboard

Additonal INFO: This happened a few days ago but I waited an 10 min and it turned on again I built the whole computer from scratch. AMD Phenom, 750W, 4GB RAM, 2 250GTS GFX

So, without any spare parts how do I tell if my CPU has failed or my motherboard?

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As you can see this is a rather difficult problem to pin point because of the absolute zero feedback from the computer, but with a working PSU – Seth Hikari Jul 26 '11 at 3:27
up vote 5 down vote accepted

You really can't without more parts to test with, but the odds are very much on the motherboard. Not that someone else may have seen more go, but I have only seen one CPU actually go bad in 17 years. I have seen PLENTY of motherboards die though.

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I also feel that it is the mother board even though it is only 4 years old and a very good ASUS, I am also thinking if the CPU was bad the computer would at least turn on a fan or something for a second or so. – Seth Hikari Jul 26 '11 at 3:23
@Seth Hikari Let's face it, in diagnosis, we always try the easiest things first, and then the most likely: Motherboard wins most likely by a landslide. – KCotreau Jul 26 '11 at 3:29
A motherboard with no CPU attached does what when you attempt to turn it on? – Seth Hikari Jul 26 '11 at 3:34
@Seth Hikari I had never even tried that, but a quick search shows that 99% of the people say "no" it will not POST (which is what I would have thought), but there may be some motherboards that will just inform you there is no CPU installed. – KCotreau Jul 26 '11 at 3:45
Just pulled CPU nothing changed, I think I have to assume it is the motherboard at this point – Seth Hikari Jul 26 '11 at 4:04

A few ideas to try:

  1. The power switch might be broken or misaligned. Depending on what kind of case you have, this might be easy or hard to diagnose. Ideally you would move the computer into another case to test this, or move another working computer into this case.

  2. Check that the power switch cable from the case is attached properly to the appropriate jumper. I know you said you checked all the cables, but this one might be hard to tell if it's seated completely or connected to the correct jumpers.

  3. Make sure there are no shorts on the bottom of the motherboard. Perhaps there's a stray screw that fell into the space below the motherboard when you moved the case?

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Thank you, I have done these things, check to see if the switch to the motherboard was bad, used both power and rest with no result. – Seth Hikari Jul 26 '11 at 3:22

I have an ASUS P7H55-M Pro mb. I also found it dead as a doornail one morning. I tested the PSU, by disconnecting everything and then jumping the green and black connections on the MB connector, PSU fans came on fine. I connected the HD containing the OS and a dvd drive. Replaced the BIOS battery on the MB. The computer booted and everything seemed to be working fine. Then it shut down dead as a doornail again. Same, all peripherals appear powered on. My conclusion is the MB is bad. In all the research that I did on this issue, nowhere did I see a suggestion to replace the BIOS battery as one of the tests.

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