Repairing an old G4 "Digital Audio" that wont boot

Hi, first post here!
I don't usually work on macs, but I'm strapped for cash and figured it couldn't be any worse than working on a Dell...
When I first power it on (I hadn't touched anything) it flickers for a few moments and then comes on, then hangs at the flashing question mark/mac face indefinitely.
I loaded the Mac OSX disk into the disk drive and tried to boot from disk (I tried booting twice, once holding down "C" and the second "CTRL") and noticed a funny clicking noise... so I swapped out the drive and started over again but no dice...

The guy that brought this G4 to me, also left a G4 "AGP Graphics" with me with a dead CMOS battery that was causing a similar but not identical issue (the first one would boot erratically, sometimes I'd get the question mark, some times nothing happened at all), could that cause a system to fail to boot every time?

It's hard to know .. firstly, what does the Mac OS X disc look like? If the disc is grey then that isn't the disc you need to start from ... you would need the Universal Disc or Full Retail Version of Mac OS X, which has a large X on the label and may be Black for Panther (10.3) and I'm not sure for the earlier version of Mac OS X.

The Digi Audio originally shipped with Mac OS 9.1 but can be upgraded to Mac OS X 10.4.1 .... we need to ascertain where the Mac is currently at, software wise.

Can you talk to the person who last used the Mac? From what you say, there could be a failed Logic Board and you've fitted a new drive so you need to tell me what format you chose for this new drive? AFAIK, you need to Format the drive as Mac OS Extended (Journalled).

You may or may not have already read the following info, but here it is:

Mac os9 flashing question mark and face - how can i get past it?!?

Using Disk Utility to verify or repair disks

How to use and troubleshoot FireWire target disk mode

Your Mac won't start up in Mac OS X (Mac OS X 10.3.9 or earlier)

the disk is black with a black "X." On the left side it says "Mac OS X Leopard ↲ Install DVD ↲ Version 10.5."

The guy (a friend) who owns both G4s, got them broken from a friend assuming I could fix them...

I think you misunderstood me, I replaced the DVD drive because original one was making clicking sounds.

I was simply trying to boot from the DVD drive so I could run a diagnostic on the hard drive but the computer seems unresponsive to keyboard commands during boot up.

I've faced a similar problem... still waiting for someone who'd help me out...
How to save YouTube videos

yeah, I'm on a deadline and none of the forums I've posted to have responded...
I'm about to just send it back to him and tell him it's toast...