Can you get into bios? If you can't get into bios but get a positive signal for the monitor you might need to reseat your processor. Have you gone into bios to see if the hdd is showing up there? Which bios is it running AMI? If it isn't showing up in bios maybe you could try a different sata connector? What do you have as the first boot device? USB for the OS install or Optical drive or hhd? Are all the parts new? Might be a bad video card if you're not getting a signal.
On a silly note - make sure your keyboard is plugged in properly and there is nothing sitting on one of the keys. Switch out the keyboard.