DVD player problems


I've got an older G4 AGP (originally with 350 MHz processor but recently upgraded to 1.2 GHz). I'm running system 10.3.9 with 896 G of memory.
Here's the problem: it won't recognize DVDs that I've burned (neither video nor data). Some of these I've burned on my G4 Powerbook's superdrive and others with a Panasonic DVD player/burner. It will play commercial DVDs with no problem.
My Powerbook G4(same operating system, 1.25 Gig processor) plays all of the DVDs with no problem.
I'm using name-brand discs (HP and Imation)--no brand X.
Can anybody suggest what the problem is? I've tried scrapping the DVD plist in my preferences to no avail.
Thanks for any advice.