Do you have a green light on the MOBO?
Check all the connections are secure.
Re-seat the RAM and graphics cards.
Is your monitor connected by DVI or VGA?
Check the tutorial I posted, you can put the Windows 7 installation on a 4GB USB drive.
What OS was installed previously?
Are you currently or planning on Dual Booting?
Check this sticky thread and try to answer all the questions you can, Questions to use for help with Installation Issues
The more information you give us the better we can understand what might be causing the problem.