Power supply shutdown within seconds of switching on

Please help. Newbuild as follows:

Asus M3a32-MVP Deluxe motherboard
Samsung SpinPoint F1 500GB SATA-II 16MB Cache
OCZ 2GB (2x1GB) PC2-6400 gold Series DDR2 (just trying with one module)
AMD Phenom X4 Quad Core 9750 2.40GHz
Scythe Mini Ninja CPU Cooler
Corsair HX 520W ATX2.2 Modular SLI Compliant PSU
Asus DRW-2014L1T 20x DVD±RW SATA Dual Layer Lightscribe ReWriter
Coolermaster Centurion 534 case
Asus ATI Radeon EAH3650

When I turn the system on, the fans spin, the hard drive seems to power up, the DVD makes noises .... and then, within seconds and before any beeps the power cuts out. I've tried unplugging various connectors and removing the graphics card with no difference. Removing the memory however results in immediate error beeps but no shutdown till done manually.

I had originally used a Gigabyte GA-MA78G-DS3H with the rest of the components the same. With that one, nine out of ten presses of the power switch would not result in any power. On the one in ten powers up I could at least get into the bios and once tried to install windows though everything went pear-shaped when the HDD was no recognised. I decided it was the motherboard and tried the Asus (having had no problems with their boards in the past).

I'm down to a few options but don't want to go out buying further new components without knowing what's wrong: CPU or PSU seem the likely culprits. Does the Corsair 520W supply enough power. All my calcs say yes. Could the CPU be fried. What else could it be.

Any suggestions would be greatly appreciated. I'm at my wits end!

Many thanks for the response. I need to take this in stages.

Bios seems to be Rev . 1 . 02G or at least that's what's printed on the board next to the model number. Any ideas where that stands in the grand scheme of things and if not supporting the CPU how the hell do I flash the bios when I don't get anywhere near the post. Thanks.

You would need a CPU that at least works somewhat to flash the BIOS.... that needs to be done, but I do not know if that is your problem.

You should do as aus suggested and verify that you have no incorrectly placed standoffs creating a short. You should also check that you have both the 24-pin power connected and the 4-pin near the CPU.

Trying a different stick of RAM would not hurt.

A very interesting development for which any assistance would be appreciated.

I dismantled the entire system as suggested and placed the mobo on an anti static mat. I plugged in one stick of ram, the CPU, cooler and video card which I connected to a monitor. I plugged in the 8 pin and the main power connector and powered up by shorting the power pins. .... voila! it started up and allowed me to get into the bios which showed it was nearly a year old (0803). I attached a floppy drive and powered up again. ... voila! things were looking good. I updated the bios to 1203 with no problems and really believed I was on to something. Everything seemed rather stable.

I then tried attaching the HDD. Powered up and ... shutdown. Exactly as when everything was in the case. I removed the SATA cable and just powered up with the HDD plugged in to the PSU. Again ... shutdown.

Seems like we're narrowing it down to HDD or power supply. So I tried another HDD which I was planning to use for creating a RAID array. Samsung spinpoint HD320KJ. Again powered up and again ... shutdown.

So at this juncture all fingers seem to be pointing at the PSU unless anyone has any other opinions. I can't find out how much power the graphics card uses but is it possible that the 520w supply is simply not enough or is it likely to be faulty?

All suggestions gratefully received.