My Mac OS 10.4.11 won't boot to the CD drive at all. I am trying to boot an Ubuntu 8.10 disc that I burned recently. I booted the CD on my MacBook v10.4.11, and everything was fine; I was able to install it with no problems. However, on my home computer, an eMac upgraded from Panther to Tiger 10.4.11, when I hold "c" (the same procedure that I used to boot from the disc drive on the MacBook) nothing happens: it just boots the Mac OS. The only difference is that there is only 1 user on the MacBook, and 5 users on my home computer. I also have tried the ctrl-option-shift-delete on the home computer, to no avail. Any advice?

The disc is a DVD not a CD, does your eMac have a DVD drive? A lot of eMacs have cd only drives, not combos or superdrives. Also, most discs that come with Apple machines are machine specific, which means the disc wouldn't install on the eMac anyhow.