My iMac G5 1.8Ghz Hard Drive has disappeared!

I was just checking Permissions, etc with Disk Utility by starting up with my Install disk and Disk Utility isn't showing my Hard Drive!!??? When I try and start up my iMac it show a flashing question mark on a Folder. I have tried starting up from Diskwarrior Disk but that also doesn't show my Hard Drive??!! :confused:

Check out this Document (http://docs.info.apple.com/article.html?artnum=58042)at Apple.