Can't get this Mac to boot

I had someone give me a G5 iMac (2006) that wouldn't boot. Being unfamiliar with Macs in general I did my research thoroughly. I still have not found a solution. What I am seeing upon booting up is a white screen with a small grey Apple logo. It will stay here until I shut it off.

I did acquire a copy of the 10.4 OS Tiger from a friend yesterday and tried booting up the disk (by pressing "c"), but all I get is the same white screen with an Apple logo in the middle. I have exhausted many resources, but am not sure I am even looking in the right direction. Any help would be appreciated.

 

That's a great thought. It never even occurred to me. Is there a way for me to figure that out without taking apart the entire unit?

On second thought.... I remember that when I started the iMac using the option key, I could see the disc in the window on the startup manager and it said "MAC OS X Install Disc" so I assumed that the drive was reading the disc properly?

 

I'm not sure I can, but does it really make a great difference between 10.4 and 10.5? Obviously you can tell you're talking to a Mac newbie. My concern is that the entire Mac seems non-responsive since it refuses to boot from the hard drive or the CD/DVD in any format.

 

Thanks for the response. I was hoping to have something where I could do the repairs myself, but what you are suggesting seems to make the most sense. It seems that the hard drive and CD/DVD drive are intact and I was starting to suspect the logic board. Obviously considering the cost to replace those parts would be a waste considering that I could get a used one in working condition for much less if I so desired. Thanks so much!