iMac G3/333 Tray-Load - Will not boot any Mac install media

Hello,
I just got my hands on a tray load G3 iMac, and I'm trying to do a system wipe with my retail 9.2.2 cd (it worked on the other two iMacs.) I have the cd in the drive, and it's showing up perfectly fine in Finder, but I'm not able to select the CD as a start up disc. Holding C at boot just leaves the machine at a light grey screen, holding opt to bring up the chooser does nothing. I tried a 10.1 retail install disc as well, with the same issue, However it will boot from a ubuntu linux CD perfectly fine. I've tried resetting the NVRAM/PRAM and its still doing the same thing. The machine currently has 9.0.4 on it. Any ideas for a solution?
Thanks

Hmm, that's very strange. There may be some sort of administrative block preventing the boot of any CD's. Which I've seen before, especially if the iMac was in a school at one point.

Are you currently logged as an administrator, or as a user? (with limited permissions)

Like I said, the machine is only running OS 9.0.4, so how would I go about checking that? I can boot into open firmware fine as well.