Katana24 3 Junior Poster

Hi - I just got a new dvd caddy for a DVD drive removed from an old laptop. I have attached it up properly and attached the two cables: USB and a power cable, going through separate USB cables to the computer.
Attaching it to my mac: the mac see's it but it doesn't run (there's already a DVD in the drive) I can't watch whats on the DVD nor can I eject the DVD by selecting "Eject" from the desktop or by pressing the button. What could be causing this?