Hi Sheryl,
Considering your DVD Player will recognize one DVD format and not another... it certainly could be the drive but before you do anything else, try trashing the DVD preference file first, it can't hurt anything.
Go here: MacintoshHD/Users/Library/Preferences. Open the Preferences folder, locate this file:
com.apple.DVDPlayer.plist Drag that file to the Trash, empty the Trash and reboot.
Also, make sure your drive has enough free drive space. Open Disk Utility (Applications/Utilities). Select MacintoshHD the in panel on the left then look below where it says: Capacity and Available Make sure the Available disk spac is a minimum of 15% of total drive space.
Also, if you don't have a good disk utility to run maintenance to empty cache and logs files... get Onyx. It's free and easy to use... it's here and the download is for Tiger:
http://www.titanium.free.fr/pgs/english.html I think it's the second download option. Install and run Onyx at least once a week to keep your Mac happy.
Carolyn 🙂