Try this.
Reset your cmos by doing the following.
Unplug the power supply from the wall outlet, remove the cmos battery, press the power button on the case for 10 seconds, then wait 10 minutes. Reinsert the battery, reconnect power. Remove the HDD, cdroms and any other devices from the PSU. Only have onboard video, 1 stick of ram, mouse, keyboard and try booting up.