problem booting from cd/dvd


i have a gigabit ethernet G4 i'm trying to install tiger on. the problem is i can't boot from the optical drive. i've tried different cds, dvds, the original optical drive. no go. the computer just goes to the gray screen with the apple, but no progress indicator shows up and it stays there. if i hold down the shift key while booting (there is no OS on the harddrive) the progress indicator eventually appears and after a long time the computer might boot of the cd, but its mega slow. i've reset the firmware, held down the c key, the option key, every key i know of. the computer knows when the media in the optical drive is bootable. any help would be appreciated.