Remove all USB devices and try again.
Make sure all the cables in the case are securely plugged in.
When the computer starts up it should mention something about pressing a key to enter BIOS setup (or configure setup options)
Make sure IDE and SATA are set to auto-detect.
if you are using a sata drive, make sure the BIOS isnt looking to boot from IDE, and vice versa.
try loading BIOS setup defaults and try the computer again.
(refer to the manufacturers support page for your system's manual for help with BIOS setup.)
If you have a Microsoft Windows disk (Not manufacturer restore disk) You may need to try booting the computer from the CD and running Windows Setup to repair your installation.
After confirming the BIOS matches up with what the manual has to say, post again if you need more help