Your g5 doesn't support command + r.
command + s Brings the machine up in single user mode. A bad sign if command + s doesn't work. Bad hd or corrupt file system.
Run hardware diagnostics. It's good for a sanity check.
Starting up the startup manager will give you a quick assurance your g5 logic board is "goodish".
The startup manager will list all of your bootable partitions then give you a choice of which to boot. Hold down the option key then power on. Continue holding down the option key until you see the startup manager. This brings up the startup manager. Click on your hd or disc. Click on right arrow key.
If startup manager is working, your harddrive is probably bad. Try a newer hd. Boot from an external hd.
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I suspect disk corruptions.
verify & repair your startup drive
To verify & repair you file system on the startup drive, you will need to run disk utility from you installation DVD.
This article will tell you how to get to disk utility. Once in a disk utility, you can go and attempt to recover the disk.
http://support.apple.com/kb/TS1417
To repair your startup drive, you will need to run disk utility from your startup DVD.
Mac OS X 10.4: About the utilities available on the Mac OS X 10.4 Install DVD
http://support.apple.com/kb/HT2055
How to run disk utility from your startup DVD.
Insert your startup DVD into your reader. Power down your machine. Hold down to the c key. Power on your machine. This will bootup your startup DVD.
This will bring you to a panel asking you for your language. Pick your language.
- You you come to the Install Mac OS panel. Do not install.
- Click on Utilities menu item. This will give you a pulldown list of utilities.
- Click on the disk utility.
- You are now in disk utility. Pick your disk. Click on repair it should be on the lower right of the panel.
- Once the repair completes successfully, you should update your permissions.