iDVD4 glitch, part 2

I'm hoping you can help, part 2.
System: Mac G5, dual 2ghz, OS X version 10.3.9; Final Cut Pro 4.5, iDVD4, version 4.0.1.
This has been a reliable system for 4 years. I produce a weekly 30 minute TV show (in standard format) in Final Cut Pro 4.5, and part of my output is to DVD. I make 4 DVD copies weekly.
Recently, when I follow the same steps as always to make a DVD, shortly into Step 2: "menu & slideshow rendering and encoding" faze, the screen freezes (or pauses) and the computer clicks and shuts down. When I reboot, I receive this message:
"You have inserted a disk containing no volumes that Mac OSX can read. to continue with the disk inserted, click OK."
I use memorex DVDs and was in the middle of a 50 pack when it first started shutting down. I have cleaned the heads, tried different DVD disks, and checked the computer display so it reads "never" on when to put the computer to sleep. I also trashed my iDVD preferences, a suggestion from David on this website. It still shuts down, almost immediately into the copy session.

ONE NOTE: It does work on a short 3-4 minute video, I have copied a few, but will not duplicate the 30 minute show.
Any suggestions would be truly appreciated.