I just put a build together today but I'm having this weird problem. The computer seems like it's on i.e all the fans the turn on, the graphics card spins but on my monitor, it displays nothing. I've also tries testing my monitor by plugging my old computer to it and it worked fine. So i guess the problem lies in my new computer.
My specs are:
Asus P5Q deluxe mobo
HIS 4850 IceQ4 Turbox
Corsair 4Gb (2x2gb) 1066mhz Dominator Ram
500gb Seagate HDD
Corsair hx-620 PSU
Coolermaster cm690 case
Pioneer dvd combo drive sata
thermalright ultra 120 extreme heatsink
Another +1 for roadrunner197069's suggestion. You might also try booting with only one stick of RAM installed if the 4/8-pin CPU power connector is in fact plugged in. My money's on the CPU power connector, though.
Easyest thing u can do is get a speaker for the mobo and listen to the post codes... i have a problem with the no video. and i tried everything until i hooked a speaker up to the mobo and found out it was bad memory. Once you hook up a speaker and if it gives u something other post code other than the normal single beep look up the bios from your mobo. and see what you get.