Often times when people copy a windows or ubuntu disk they mess up the boot sector so their cd is not bootable. Are you using a factory made or home made boot disk? If the cd is home made google a boot cd guide and check your settings.
Go into your BIOS, if you have multiple drives, you need to manipulate the drives so the ones you want to use as boot can be accessed by the BIOS, and this goes for both HDs, and DVDs, I ran into a similar issue when I got my SSD and was installing it.
For instance, if you have multiple DVD burners, set one as drive 1, and the other as drive 2, and then set the boot priority of drive one to be first.
Then same with your HDs, set one as drive 1, one as drive 2, one as drive 3, etc, then set the boot priority of drive one to be first.