The BIOS is not detecting the boot devices... see if changing the SATA controller settings helps. Try AHCI first and IDE Native second. Also check the HD and optical drive connections... check the data cables on both ends. If nothing works, reset the BIOS... Turn the PSU off or remove the AC power cable, remove the BIOS battery, press the power button and hold it for a full minute, and wait for 5 to 10 minutes before putting the battery back on and try booting the computer.