...
here's another sample. Perhaps looks similar to your cases. I'm using an MSI 945PL-Neo with processor Intel Pentium D 2.8 Ghz + memmory Dual channel 1 Gb+ MSI Nvidia GeForce 6600 (video card) + Enlight PSU 500 W.
The problems occur 3 months after my friends using it. The problems look similar to your case, when i turn on the pc, the processor fan kicked for a sec, and the power LED flashed on, and then went off almost instantly. I tought it was because the dust, then i try to clean it off, but still, nothing happens. I Tought it was the PSU, then i try to replace the PSU and i try the old ones in another PC. The result is, that the old PSU turns out to be OK in another PC, instead the other one shows nothing, i mean nothing change when i put on the new PSU on the MSI board. My Conclusion then the board is damaged (tough my friends didn't use any overclocking system on that PC) and then i replace it (Still got a guarantee), and the problem solves.
Perhaps you need to replace your boards too, tough it's a new one, but there is no 100% guarantee it will go smoothly.
What i'm trying to tell is, it is good to use a good and pure watt PSU, and it is good to use a great brand hardware. But still, a factory failure is something that we cannot avoid.