G3 CD/DVD drive stopped reading CD/DVDs

Hi, the other day the CD drive in my 12" white G3 ibook stopped reading CD & DVDs. The whole computer froze after trying to rip a CD in itunes and now it just thinks, clunks a bit, then ejects!

This also happened in my G4 powermac some time before the HD stopped working, but was fine after the HD was replaced.

Any know what might cause this and what the remedy might be?

thanks.