DVD cd-rom malfunction

Hello,
Thanks in advance for help!
Have HP Presario V6000; Model 6205NR with Matshita DVD-RAM UJ-850S ATA Device. Laptop purchased with Vista (didn't like it) reverted back to Win XP Pro. Only problem known at the present is DVD/CD-ROM does not recognize ALL media when inserted (light comes on). I do NOT get any error messages. In my testing it will play (sample downloaded files) .wma, .asf, .wmv, .avi, .mpg., Played.wav on disk no other purchased music disks. Will not play .mp3. Will not read program disks; i.e. XP program disk. From my computer it will not read disk; sometimes it will disappear from my computer when I try to access DVD/CD-rom drive. Comes back after restart.

With DVD (purchased movie) using Windows Media Player get message "cannot play DVD because a compatible DVD decoder is not installed on your computer." I have concluded I need to purchase plug-in. If right, any suggestions? And will this fix problem playing audio and data disks?

I checked Registry for upper and lower filters. Found upper only no lower filters. Have not deleted any.

Don't know where to go from here. need help. Thanks