Won't post

I am new to building computers and have run into a problem. When I push the power button nothing happens. The mother board has a LED and that is on but other than that nothing seems to be getting power. I have spent 3 hours last night making sure everything was plugged into where it is supposed to be. I am just not sure what could be the problem. After work I plan to take a paperclip and connect the green wire on the pin connector to one of the black wires. Any other ideas would greatly help. Here is the rig:

PSU KINGWIN|ABT-600CW 600W RT - POWER SUPPLY
CASE THERMALTAKE|VA3000BWA BLK RT - CASE
MB ASUS P5LD2-VM 945G 775 - MOTHERBOARD
VGA XFX 7600GT XXX 256 PV-T73G-UDD3 - VIDEOCARD
MEM 1Gx2|CORSAIR TWIN2X2048-5400c4 - MEMORY
CPU FAN COOLERMASTER|RR-LCH-P9E1 RT - CPU FAN
CPU INTEL|PD 940 3.2G 775 2x2M R - INTEL CHIP

Thanks

P.S. Does it matter that the memory is 675MHz and the motherboard is only rated up to 667

I was able to get another power supply to test with and it works, must have gotten a bad supply.

Someone gave me a computer today and the thing was Filthy (it came from a scrapyard, the office, but still). I was testing it out and it died on me while I was using fdisk. While I suspected that it might have been due to fdisk, I had the same trouble as you, no boot, no fans, nothing but a little green LED. I'm going to try the paperclip trick tomorrow when I get a chance. I've got parts from another computer I'm going to cannibalize also.

BTW, I was suprisingly impressed with what it was. Socket A (462) - Athlon XP 2000+, 256 MB and a 512 MB RAM chips (not sure what kind). I saw some onboard VIA chips, and I *THINK* an AGP slot (like I said, it needs cleaning). This leads me to my next question... how can I find out what motherboard it is? I'm going to take a close look when I clean it off... I may just remove it completely from the chassis so I can get a good look on the backside. I did some looking and it looks very similiar to the VA-20 from ABIT (http://www2.abit.com.tw/page/au/motherboard/motherboard_detail.php?pMODEL_NAME=VA-20&fMTYPE=Socket A) except I don't recall seeing USB or ethernet on it. Anyway, any suggestions?