If the drive cannot boot, there still could be some data available on it.
Example: if the breakage happened in a sector where OS X is, it won't boot, but the data could still be OK. So, you may still use this drive as an external and try to crawl it and pull stuff out of it.
If the HFS sector got hit, you are SOL and there is nothing you can do.
- Get a new drive, install OSX
- Get an external enclosure for the busted drive and try to connect it to your G5 and see, if it mounts as an external disk. It might.
If you have another Mac and a spare FireWire cable, you may as well try this:
- Connect both Macs with Firewire cable
- Start the good Mac
- Start the busted G5 and hold T while starting it up - it should boot into Target Disk mode and act as a simple external FW HDD
- the G5 should show up on the other Mac as an external HDD. If it does, crawl whatever you can and start salvaging your user folder.
- If it doesn't, you are SOL
In any case, I hope you have a recent backup of all your data.
If not, now you know why the rest of us do. :-(
Now all I get is a white screen with the Apple logo and the gray timer circling.
If you get the gray apple logo with the progress indicator gear turning, then your computer is actually seeing the hard drive and is trying to load the system. (If it wasn't seeing the boot volume, you would be getting a flashing icon of probably a broken folder or something similar from the firmware.) That's a start, in any event.
There are a couple of easy things to try. First and foremost, do a PRAM reset by holding down the cmd-option-P-R key combination at boot until you hear the second chime. Second, you should try a "Safe Boot" by holding down the shift key while booting. This will make a run at repairing minor problems in the boot volume by running fsck (a Unix file-system check and repair command) and then loading only a basic set of Apple kernel extensions.
Not saying this will work completely, but often it does. The next thing to try would be a verbose boot by holding the cmd-V key combination at boot until you hopefully get to a Unix terminal screen where the system reports what it is trying to do. If you get that far, then there is information there that might be helpful.
I noticed now that the Hard-drive itself has a louder than usual fan sound.
You are probably actually hearing the computer's fans ramping up to full speed when the system has not loaded and taken control of the machine. This is a safety feature built into the PMU/SMU.