Do you have your CD/DVD set to first boot in the bios? Check your "Boot Device Priority" option under the "Boot" tab. Also, is your CD/DVD your are trying to boot from the master? If none of that work check your power connection and try a different SATA/IDE cable.
Occasionally some discs won't read in a given writer, I burned a slipstream disc recently and it would not work in my main machine (though one of those drives refuses to read any cd now). So try another standard disc if you can.