3d Mercury turns on then turns off in a few seconds

[Dark Mantis]

So it does seem that the PSU was faulty then!   Priceless!

Whether it has damaged any of your other components wont be obvious until you get a replacement PSU.

Well the first thing is to change your PSU. Never buy a cheap and nasty power supply they can go wrong and take out all you other expensive components at the same time. Not only that just because it is marked 600W often they are nowhere near that rating. Purchase a good make like Seasonic, CWT, Corsair, Thermaltake, Enermax, Gigabyte, Coolermaster, Antec, etc and try and get one with a single 12V rail if possible. I would advise you to get one of about 650W minimum depending on your hardware demands.

[jonathancolledge]

Could the problem have caused your power supply to fail. If so it isn't the power supply!

I have exactly the same problem.

I changed the power supply - same.

Swapping the reset and power buttons worked with new power supply.

I dare not leave it on in case somewhere, something is touching the case and causing some badness thus overloading the PSU.

Any ideas? I don't want an explosion!

[jonathancolledge]

My first thoughts would be that there is an extra motherboard post left in from the last build in that case. It is causing a short to earth via the chassis. It is possible that something else could be causing the short but that is most likely.

Ah - this might be a contender. Could a short cause the PSU to fail? I would have guessed so?

[Aussie Allan]

  YUP!....Can take months .... or Seconds

  When PSUs go big time ... they usually take something with them .... Nasty little sods ... this is why it pays to go the quality route!

  Aussie Allan

[Dark Mantis]

I would agree and anything that is putting an exceptional load on any of the busses of a PSU can cause failure down the line. On rebuilds where tha case has been used previously extraneous  motherboard posts are quite common. Of course there are other ways that a short can occur. I had one member on the forum here quite a fdew months ago now that didn't use any motherboard posts at all and just screwed the board to the backing plate directly and wondered why nothing worked!!!!

[M0rningLightM0untain]

Hey I just want to note I've been experiencing a similar issue.  When I power on, case comes up for about 3 seconds then shuts down.  After 2 seconds, it magically boots up like a charm (without me pressing a button again.)  I will post more detailed info later.

[Dark Mantis]

Hi and welcome.

Try doing an extended clear of the CVMOS followed by loading Optimise BIOS Defaults then synchronise the two BIOS versions. Follow these instructions exactly and you should be fine.

Remove the power cable from the mains supply and then press the power switch on the case for a few seconds just to drain any residual energy in the PSU capacitors.

Once done remove the motherboard battery for at least one hour before replacing it.
 
Next plug back into the mains supply and boot.
 
You will now need to enter the BIOS by pressing DEL and load Optimised BIOS Defaults.

Make any other changes to the BIOS settings to suit your self like disabling the floppy drive, disabling the full screen logo and making the HDD the primary boot device and then press F10 to save and exit.  Power down the computer.

If you have a PS2 keyboard connect that instead of the USB version as it is more reliable.

From a cold start with the power to the machine switched off press the power button and then enter the BIOS by pressing Del.
 Then when you get to the main screen press F9.
 
This will bring up an extra screen which will display more information about the two BIOS versions. Assuming they are different exit the BIOS and shutdown.

Again press the power button and this time press Alt + F12 where you would normally use the Del key to enter the BIOS. You will find that then your monitor will turn black and you will see:

Press [Enter] to start copying main BIOS to backup BIOS...

When you press Enter more text will appear saying:

Writing BIOS image.... xxxKb OK

Once completed more text will show:

BIOS successfully recovered! Power off or reset system!

Do as it says. Both Main and Backup BIOS chips now store the same BIOS version. You can now reboot as normal.