installing ubuntu on a g3 imac

ok I made a boot disk of the proper version of ubuntu, I load it in the cd drive, restart the imac, hold down “c”, it boots, a command prompt of sorts comes up and tells me to press enter, i do, the ubuntu logo comes up on my screen along with a load bar, it loads, the hardrive spins away, and then the screen goes black and nothing happens. whats going on? I left it in this state for a good day, nothing happened! and when I restart the computer nothing on the hardrive has been touched. anyone have any suggestions?