Make sure your monitor works and its all plugged in. Try resetting the CMOS. I had the same problem, but I didnt have onboard video. My PCI card wouldnt work for some reason, so I took it out and replaced it with a new PCI-E and it worked fine. My only suggestion is to try an ad-in video card.
EDIT: Another thought, if it's not beeping, it means the compputer isnt even starting. CPU or mobo could be bad. It should beep if the RAM was bad so I dont think thats the problem. Try swithching the CPU with one that you know works. If that doesn't work, RMA the mobo.