G3 no boot manager

Hi,
I've got a Power Mac G3 and I want to install linux onto it however I'm having some problems. Everyone says hold down C or Option to load a "Boot Manager" but when I turn my mac on nothing happens, I've tried everything including T for firewire mode but it just skips and starts tiger. The disk appears once tiger has loaded but I can't access the disk at boot up.
Weirdly though I was able to get something before when I did this. It was a question mark in a folder blinking which then disappeared 10s later. So I tried resetting the PRAM and that was successful but now the folder doesn't show up and i'm back to nothing.
What can I do to fix this?
I just need to be able to boot from the internal CD drive or preferably and external USB DVD drive.
Your help would be very much appreciated,
Sephers.

Well give up on the USB as only Intel Macs are bootable from USB and then USB2. PowerMacs will boot only from Firewire external drives. To boot from an install disc, pop the disc in and reboot.

Immediately after the chime, hold down the 'C' key until loading commences and then you will have booted from the install disc.

If your done with OS10 it may be easier to wipe the drive"reformat it" then
install Linux. Make shure your Linux version is for Powermacs.