Weeeeird boot error

Not sure if im posting in the right forum but im having some weird issues with my imac g5 with isight (20"). I recently bought this computer from a friend that moved overseas and didnt have their password etc. I tried to boot up with the tiger install disk to totally format & reinstall, with no luck.

I then tried plugging a powerbook in and using its cd drive via firewire and the imac would not boot from the dvd still.

Then i put the imac on firewire and loaded it as a drive on the powerbook. I then formatted and installed tiger using the powerbook. I turned on the imac and it would not boot into tiger (it stopped as a circle with the cross through it).

Weirdly enough, however, i can boot the powerbooks operating system via firewire onto the imac and conversely i can boot the imacs now installed operating system on the powerbook. But i cant get the imac to boot the OS by itself!

I have pretty much exhausted all options. ive tried booting the install dvd from an ipod. ive tried booting the dvd through the imacs dvd player, but install via the powerbook.

it used to at least get to the login screen, before i formatted, so i cant seem to isolate what the problem could be.

confused much? i know i am haha

any ideas would be greatly appreciated. im tearing my hair out!

Give the steps here a shot:

http://docs.info.apple.com/article.html?artnum=106464

Have tried this:

2) File System Check - When booting up your computer hold down the Apple Key & the S key and it will boot into single user mode. When the text is done loading on the screen type in /sbin/fsck -f and hit enter.
When that is done if it fixed things then do the check again to make sure it is cleared
When finished with that type in exit and it will start the computer in normal mode

also when i press x on startup i get this

and i get a mac os 9 folder with a flashing question mark.