Go under the Apple in the upper left hand corner to "about this Mac". more info > Hardware > ATA and see if your Mac still sees the drive. If not you may need to replace it. An alternative is to get an external optical drive. To can also start it up in Target mode if you have another Mac and use Disk Utilities on the other machine to handle this G4s hard drive. Here's how to do it: http://support.apple.com/kb/HT1661