I suggest you play a DVD with VLC PLAYER as we discover what software you used to use.
Dell Dimension 8200
I have a LG GSA-H55L DVD burner that once worked fine but now won't play most DVDs. It reads data cds, plays audio CDs and some burned DVDs but not commercial DVDs. When a commercial DVD is inserted, Windows Explorer or My Computer just lists it as "DVD-RAM Drive" as if no disc was inserted. Media Player Classic or others says something like no DVD inserted.
I sometimes put new software on this computer. It's been awhile since I previously played a DVD so I'm not sure when it stopped working or if it was a result of something I did or a Windows update, etc.
Things I've tried:
Updated firmware on the drive
Unistalled it from device manager and rebooted
Un/Reinstalled the software for it
Ensured that the IDE channel was set for DMA (currently Ultra DMA 4)
Ensured that the region code was set to 1 (as are my DVDs)
Updated system BIOS
I also tried moving the drive to the slave position on the same IDE2 and moved my second HDD to the master. Normally, both hard drives are on IDE1. This machine is supposed to use cable select and all jumpers are set to that. 80 wire cables too.
I noticed that the BIOS picked it up as "CD-ROM" not DVD. Don't know if that's normal. Device manager lists it as "HL-DT-ST DVD-RAM GSA-H55L".