If the computer doesn't POST then you may have corrupted the BIOS. get the system back to the original config that worked, and then making sure your Power Cord is Unplugged and the PS switch is off, take out the CMOS Clock battery (Button battery) for 1 Minute. Then re-install. Plug in and Power up. if it still doesn't POST, then the easiest thing to do is get another BIOS chip from an Identical Mobo, or go to the BIOSMAN website (there are others.) you can send them the Chip to reprogram for about $20.