see if you can get to the startup code by holding down the control and s keys after you power on the g5.
if you can and the code starts popping up on screen and release the keys. within that code there are a couple of lines towards the bottom that will say "if you wish to reboot:" and the code following that needs to be typed in exactly as shown.
also bing or google your answer alot of info is out there on youtube as well.
good luck!
here's something new i didn't know. i guess you could try this:
You can enter Open Firmware by pressing the key combination
cmd-opt-O-F
just as you power on a Macintosh. The
cmd
key is the one with the Apple logo, and the
opt
(option) key is the same as the
alt
key. You should see a welcome message and some other verbiage, and should be dropped into a prompt like the following:
ok 0 >
You can continue booting the machine by typing
mac-boot
, or shut it down by typing
shut-down
.