Help! G5 PPC boots up and says "can't exec /bin/sh for single user: No such file or directory"?

Help! I have a G5 PPC running on OSX 10.4 I did a .dmg reinstall from an external. Now when it comes on, after the gray apple screen, the screen goes black and says "Launched: can't exec /bin/sh for single user: No such file or directory" and the fans go crazy at full speed. I can't eject the dvd, can't start in safe mode or anything. I tried typing in commands to use fsck but no luck. Any help. I think my .dmg had a missing file.