I just built a new computer using the following components:

Motherboard ASUS M2N-SLI Deluxe AM2 NVIDIA nForce 570
CPU AMD Athlon 64 X2 4800+
GPU XFX Geforce 7900GT
Hard Drive WD Caviar 160GB 7200RPM 16MB cache SATA
RAM Crucial Ballistix 2GB DDR2 800 240-pin
PSU Antec Earthwatts EA380 ATX 12V 380W
DVD Drive Samsung 20X DVD+RW SATA w/ lightscribe
Cooling OCZ Vendetta CPU Cooler

I put all the components into my case and double checked EVERYTHING! when i finally powered it on, everything went on for 2 seconds and then shut off. all case fans, GPU fan, CPU fan, DVD drive light went on, and the HD started to spin, then shut down. I checked everything again, and tried once more. same thing. The computer would turn on and then turn off again. I switched the RAM to different slots, tried a different hard drive, disconnected the card reader and DVD drive, and nothing changed. Then, i put everything back in and double checked everything (especially my power button connection) and tried to turn it on again. NOTHING. now, nothing will turn on at all. When i switch my PSU on, though, the little green light on my motherboard goes on and my USB card reader's little green light goes on. so the computer must be getting power, right? I'm not sure where to go from here-- i am right about to buy a new case because i get the feeling it might be my power button (i took the front cover off the case to access the little button itself, and it seems everything is working though).

can anyone point me in the right direction here?

Looks like a Power Supply failure to me.
The standby lights are powered by a different part of the supply.

It may also be that you attached the heatsink to the processor incorectly. IF that happens, the chip will overheat and the system will shut itself down to prevent damage.

Billy3

Besides what Billy put, did you put the copper stand offs between the motherboard and case? They keep the motherboard from touching the metal on the case and shorting out the board. I made this mistake when I first built my computer and ended up frying the board, hehe.