Oct 7, 2011
Hello, long time reader first time poster.
I'm at my wits end having spent all day building a low tech pc for my parents, only to find the ah heck refuses to start. I've come to the conclusion that possibly a RMA is required for one of the components, the only problem is trying to identify the guilty piece. It's only my second build but the first one went perfectly (over a year and no issues what so ever fingers crossed) so I was confident it could be pulled off again, but no such luck.

(I took precautions to avoid EMS by using an anti-static mat and a wrist strap attached to the case, exactly the same as my last build.)

Note! These are all brand new and from

Asus M5A78L-M LX AMD Socket AM3 8 Channel HD Audio mATX Motherboard
AMD Athlon II X2 260 3.2 GHz Socket AM3 2MB Cache
Corsair 430W V2 CX Series PSU
Black Micro ATX Case - No Crucial 4GB (2x2GB) DDR3 1333MHz/PC3-10600 Memory Kit CL9 1.5V
(Onboard Graphics Card)

[Excuse the rather basic components, but this was a cheap replacement (or intended to be) for an aging 7 year old pc.]

The computer will begin to boot before cutting out almost instantly. Prior to this it was possible to hear the faint hum of power running through the PSU, however when the computer cuts out, the PSU also stops and does not come back on until it has been disconnected from the mains for a few seconds. The fans attempted to start but stopped in the same amount of time. The power button on the front panel also lit up for less than a second.

There is no audible bleep sounds but the LED light on the motherboard is green even when the PSU appears to stop working. I have tried this with everything connected initially, and then only attaching the minimal amount of components whilst out of the case. I have not managed to see anything on screen when the monitor was attached.

I have read through and followed the holy grail at , so hopefully that lets you know what i have done.

I understand faulty PSUs make up the majority of boot issues, so I went ahead and tested it ala method of sticking a paperclip in the PSU connector and testing it with a fan. Both the PSU fan and the case fan spun round for the time I left the power on. I'm not sure whether this rules out the PSU, but it definitely does work.

Front Panel
This can be ruled out as I used a screw driver to power on via the motherboard and still had the same reaction. So that excludes the power button being stuck in.

Whether in or out of the case there is no difference, so that rules out the motherboard shorting out due to contact with the metal surroundings at least.

There doesn't seem to be anything visibly wrong here, both it and the heat-sink have been installed and connected according to the instructions

Like the CPU, there is nothing visibly wrong with it. I have tried removing the battery for 5 minutes as well as clearing the RTC RAM as instructed in the manual.

I have tried all configurations, each slot with each RAM individually, as well as both together. There are only 2 slots on this motherboard.

Help me, please!
Ideally I would like to avoid taking this to a shop to have a look at, as I was really intending to cut down the costs. I have spent hours googling haphazardly and coming up with many pages of information that were similar to my issue, but didn't really help enough to give a clear answer.

If anyone has any idea what component could be causing my problems, just from my brief description, I would eternally appreciate it. I am sure I have failed to explain everything necessary, so just let me know and i'll edit this post.

Thanks, Matthew


Aug 3, 2011
In the past I've had the same symptoms and it turned out to be a combination of bad motherboard and PSU. I'm not sure if a bad motherboard fried the PSU or the other way around. I also did the PSU test, but it was still bad.

I would try a new PSU on your motherboard. If it boots fine, then it is the PSU. If it fails to POST, then it is probably the motherboard. When you get a new motherboard if it still fails to POST, then the PSU might be bad too.

Assuming you have a motherboard speaker, if you power on your motherboard with only a CPU then it should beep continuously since it will be complaining about the RAM.

Oh, as for that light staying on after the PSU shuts off, that is because capacitors store the energy and LEDs don't take a lot. If you hit the power button with the PSU off/unpluged it should discharge the capacitors. You should always do this before working on a computer.

EDIT: I should have said a known working PSU. So take the one out of your computer and put it in the new build. Using a new PSU you could still have a bad PSU and just really bad luck.
I'll agree ... check the mobo with your old PSU and see if it at least boots up.

the mobo is a nice choice -- it will take the new bulldozer 95W Chips due out in a few days, so RMA both the mobo and psu as needed.


Oct 7, 2011
Okay, i'm an idiot. After testing out the PSU on another systems, and vice versa i realised i'd plugged the pci plug in instead of the CPU power plug......
Thanks for all the advice, anyway
You were lucky. Interchanging either plug results in shorting 12 volts directly to ground. The PSU detected the short and electronically shut itself down without frying any components.

The plugs are polarized differently. You were not supposed to be able to plug them in the wrong place.