As stated, my suspicion was that my PSU failed suddenly last week. My girlfriend was typing a paper for school when we heard a "POP" come from my case, followed by sudden shutdown. No response whatsoever power-wise. So I ordered a sweet new Seasonic 330W PSU from Newegg and put it in myself when it came. After having hooked it up, I get no case LEDs, no case fans, no response whatsoever other than when I turn the I/O switch on on the new PSU, the green LED comes on on my Motherboard.

Being that I can't find my motherboard manual, and I can't find the LED trouble codes on the Asus website, what do you guys think my problem is? My Motherboard is an Asus P4P800 Deluxe. The LED is flashing at a constant rate when I turn the power on, probably once every second or a little less.
HELP!

It's quite possible that the PSU took the motherboard with it when it blew.

Unplug all peripherals - CD, HDD, any PCI Cards, and if it still won't post, then the board is gone.

S478's are only available 2nd hand, so it's either time to upgrade, or search Classifieds / EBay.

i agree, take out the ram and see if it will beep if not then the power supply probably took the motherboard with it

Very possible. Remove anything that is non essential (HDD, CD w.e.) and attempt to boot. If it doesn't post than it is the motherboard.