Asus A7V266-E MOBD Won’t Power Up

I recently installed a new Asus A7V266-E with
an AMD Athlon XP-1600 and 512MB of PC-2100
DDR SDRAM. Also installed a new 400 watt ATX
power supply. The system power LED light on the motherboard lights up when the power supply is switched on, but the power on button has no effect. Shorting the power button pins at the motherboard header has no effect, either. Using a Diamond Viper 770 AGP
video card and a SoundBlaster Live! X-Gamer audio card. What else does the “system power”
line feed? Ifthis line is shorted somewhere,
where can I look for the problem?