DVD-RW doesn't boot (Gigabyte MB + 2 hdds)?

Well you cant set a SATA to slave..their all masters...one drive, one port, The IDE ribbon cable has 3 connectors two close together. the end one of the close ones goes to the HHD set to master the second connector goes to the DVD set to slave. Set the Bios for CD as first boot, HHD as second boot. if you don't have the OS disc in the CD drive before you start up, the computer will just search the next drive till it finds something to that will boot up to. If it finds nothing, it asks were a bootable drive is.