Combo drive disappeared... any ideas

Hi there I have a Mini G4 1.25 running OSXtiger. I replaced the HD since when the Combo drive has disappeared from the system profiler. The drive accepts CDs and spins up but thats all... the CD doesn't show on the desktop and I can't even eject the disc using all the usual tricks. Everything else works fine (I loaded system via fire wire). The combo drive itself is OK as I've tested it (and recovered the CD) by putting it in another Mac Mini. PMU and PRAM reset.... no change! Any ideas??? Thanks