I'm leaning toward a hardware problem since it is a g5: bad capacitors or bad video card.
You may want to run these "standard" fixes if the problem persists. Run in safe mode for awhile. If this works, you have a video chip problem, and can change to run safe mode video drivers.
1) Check the amount of free space on your harddrive. You should have a several gigs free.
2) You should run disk utility
a) verify the disk
b) update your permissions.
3) Try a safe boot.
Shutdown your machine. Hold down the shift key. Poweron. Wait awhile Wait awhile while you harddrive
is being checked.
4) You may want to run applejack to clean up your machine.
5) Run hardware diagnostics. It's good for a sanity check.
a lot more ways to fix your Mac.
Thanks for reply.
So, I have booted in safe mode, had a kernel panic there; booted from cd to run disk utility and about a minute into running repair, had a kernel panic; booted in single user mode, ran fsck command again - no problem again, so typed reboot and ....nothing. Again.
I then tried to boot in safe mode again and got another kernel panic.
I have 23G free space. Is applejack something I need to purchase?
Your machine crashing when booted from a cd/dvd points to a hardware problem.
I've heard that if you take you G5 to an apple store they will look at the capacitors & tell you if they are good or bad.
Google: g5 capacitor replacement kit
Have you run disk utility fix permissions?
While the file structure on the disk is fine, you could have some file that is wrong and this file is causing you machine to crash.
You may want to consider a archive and re-install mac os x. There is an option to save all of your data then re-install the operationg system -- Mac os X.
You should backup all of your data.
AppleJack is free.
I agree. I had the same problems and the capacitor replacement resolved my issue.
I performed this on an imac isight (not as easy to disassemble).
I ordered the capacitor kit from jimwarholic.
If you plan to remove the copper tubing (I did but not sure if needed to) then you should order the small thermal adhesive to use before reattaching.
It hasn't crashed since.
You need to be handy with soldering iron to perform the surgery.