Leopard disk not recognized by G4, etc

[bigjer]

This is a long story. My G4 Silverdoor Dual 867 MHz PowerPC, 1 GB SDRAM, has been giving me a variety of problems.

Currently:
1. The PHILIPS CDD5101 DVD-R, CD-R,RW drive refuses to recognize the Leopard install disk. Furthermore, if I startup with the DVD(?) in the drive, the computer fails startup, getting stuck at the Apple image on greyscreen. If I try SingleUser startup with the DVD in (in order to run AppleJack) that fails just after noticing the Philips drive; screen locks up; Return/Enter has no effect. (Forcing shutdown, then starting again with mousedown succeeds in ejecting DVD, allowing startup.)
2. I connected my Powerbook via Firewire to try to install Leopard via the Powerbook drive, but the SilverDoor refuses to startup in Firewire target mode.
3. AppleMail has lost its ability to Reply or to Send a new note.
(AppleJack works if the Leopard DVD is not in the drive.
Computer starts from the drive with DiskWarrior in it and DiskWarrior replaces directory successfully.
Neither of these fix the problems.)
4. I'm having big trouble typing into the "ask a tech" text box. I have to type it in TextEdit and copy/paste it into your forum because the page keeps disappearing as I type.

Transition:
I had erase-&-installed Tiger again, updated to 10.4.11, and used Migration Assistant to migrate Users and Documents. Migration Assistant refused to migrate Applications. ("Applications" in Migration Assistant showed a many-digit negative number as "size.") I copied my Apps from backup by hand. They all seem to work ok. Even Mail was able to Reply and Send for maybe an hour or two.)

Prior to transition:
All the "currently" problems existed.
Shortly after installing the most recent QuickTime update, Finder began to spontaneously quite and relaunch every 90 seconds, forcing Finder windows in front. Changes in Finder windows didn't save between relaunches.
(Erase-&-install fixed the Finder problem.)

Can problems 1, 2, 3, 4 be connected? With a single solution for all four? 1 and 2 seem perhaps to be hardware breakdowns, but 3 doesn't, and 4 just appeared. . . . This is kinda scary.

[MisterMe]

Is this the retail version of Leopard?

[bigjer]

Ordered from and shipped by the Apple Store.