Booting to nothing

My computer will not go through it’s startup routine correctly when I boot. Sometimes when I boot, the monitor stays in sleep mode and the computer does not beep. Nothing really happens except the hard drive hits and the cd-roms hits once and then that’s it. If I unplug the computer and wait 15 seconds and plug it back in, it will then boot. Sometimes I wonder if it isn’t the power switch itself? I just bought and installed a new 400 Watt Antec power supply. I have an Asus A7V Mobo and a 1 GHZ Athlon w/256 Mb RAM.