Let me get this straight: New power supply and motherboard? Did you plug in the 4 pin 12v rail? The only other issue is the CPU itself. I would break down that system to just the mobo and CPU/heatsink+fan. if it will power up then you need to start adding components until it fails and then you will have the culprit. If that fails you will need to do all of the above but take the mobo out of the case. One of your components is shorting and causing your system to power down. The bios will shut down for all errors at POST. It may very well be a dead CPU.
Noli Nothis Permittere Te Terere!!
EVGA 680i, Dual EVGA 8800GT'S (650/950), 4 gigs OCZ DDR2 1066, Intel Q9450 at 3.8 Ghz, Koolance Water Cooled, Dual Plextor16x DL DVD+/-RW. Dual WD 250gb 16mb Cache Sata 3.0. 3DMark06 score = 19,168.