i got a psu for 20 bucks - its an ultra x connect modular psu. cmos are normal. does the cpu have to be under a heat sink for it to work - i was just trying to get it to turn on

hi - i recently built a rig heres the spects

500watt psu

core2duo

p5n - sli asus mobo

2gigs - cheap brand ram

exelstor-160gb hdd sata2

3870 saphire radeon

dvd burner

ive connected everything correctly and 500 watts is definetly enough power for my system and an led on my mobo shows it has power but when i press the power button the l.e.d.s flicker and thats it. no fans turn on, nothin except my case leds whats wrong? also there is no beeping so its not ram or video card. - i tested all my components iduvidualy except cpu(which probly works) but i cant find the prob please help!