Motherboard/CPU fried?

Ok, this might be a long story...

I have a custom built PC with the following specs:
Asus P5WD2
Pentium 4 3.8GHz Processor
2GB Corsair RAM
2x 6600GT Cards
2x 250gb SATA disks
2x 320gb SATA disks
2x DVD-RW Drives (IDE)
Antec 550W Truepower PSU

Which had been running nigh on perfectly for the past 2 years. Then it started to have trouble switching on from cold. i.e. If i shut down the PC, it wouldn't come back. It always restarted fine. And I always have the PC on anyway...

On saturday, we had a power cut. I ran upstairs to turn the PC back on, but no joy. It just wouldn't start. I then went through and checked everything, stripped it all down, still no start (there was a light on the motherboard, but nothing started up). The power supply had a slight burning smell, so I replaced that on Tuesday night with a Jeantech 600W supply from PC World (i was desperate!)

This worked! I plugged it in and it all started up, got into windows and I was resetting the fans (bios has been reset so put them back to optimum settings) and it turned off. I pressed the power button and the PC started but with no signal on the screen. (To make this whole thing more challenging, I don't have a system speaker...) I turned the PC off again and then pressed the button and nothing. All I get now is a slight movement from the fans. I then took the PSU back to PC World and got my money back (hoping that it had died because they're such a bad shop). I bought a Hiper 580W PSU which arrived today. The problem is the same...

If I remove the EATX12V plug, the fans all start and there is power to the DVD Drives. With the EATX12V plugged in, I have tried with no RAM or GFX (the PC should start to an extent?) but still nothing other than a brief blip of power. My question is really whether it is going to be the motherboard or the CPU? I tried removing the CPU and booting and there is slightly more power (the LEDs come on on the new power supply) but then it stops. Neither the motherboard or PSU are that expensive but are difficult to get hold of (a mobo went on ebay 2 hours before mine died :@!).

Any ideas/way to tell for definite?

I have tried pretty much everything I can think of/have read. Clearing CMOS lots and trying on non conductive surface etc.

As far as i knew you had to have GFX and RAM to get any sort of boot?

That said I saw this on an older PC, after much digging around and trying of difference things I took off the CPU, lo and behold a charred melted mess on the top. Fingers crossed for you mate!

I would think that there is something pulling down the PSU power supply rails and causing the PSU to shut down - and since the PSU starts with EATX12V plug removed, that is likely to be the problem area. So I would suspect the MOBO. The easiset way to test it is by substitution though if the mobo is hard to come by that may not be an option. can you connect a system speaker to the mobo to see if you get any sort of POST code if you boot the PC without the EATX plug - if so that would show that the processor is OK.

Final update! I bought a new motherboard off ebay for £45 and it worked a treat. I have all my data on the raids still and everything! I believe the PC World power supply blew the motherboard (I will never buy from there again...)

Thanks for the help