CD/DVD drive error

i've got an old pentium3 that i've just starting using again for the dvd player. the drive will read data discs and music cds but when it comes to dvds, i cant watch the films. i can explore the dvd files but the software i am using acts as if there is no dvd in the drive. i reinstalled the software and tried using completly different software but this has no afect. anyone got any ideas.

What is the DVD drive and what software are you using?