Ok, will need a moderate amount more information.
First off, you do have all the rest of the parts assembled in the computer correct?
When you power the computer on does any lights on the outside come on?
Is there a light on the motherboard, and does it come on?
Do the fans inside the case turn on?
Do the hard drives and cd drives power on
Does the monitor say no signal, or do you just get a blank black screen?