PC internal DVD player problem

[gumboil]

I've got an NEC 3500AG DVD burner fitted to my XP Pro PC at home. For no apparent reason over the last few days, it's decided not to recognise discs intermittently.
When I put a film DVD into the drive, the drive no longer auto-runs and doesn't start up the WinDVD or PowerDVD software. A music CD similary, does not activate Windows Media Player.
When I attempt to check the contents of a DVD or CD via My Computer, the disc appears as empty with no files on it at all.
On the odd occasion, a DVD works normally when put into the drive and shows the files on dic or plays the disc without my intervention.
I think this behaviour first started when I inserted a DVD with a number of films burnt on it that had been downloaded from a torrent site. The film formats were all "dvdrip aXXo" files and the default player on my PC was DivX Player. Again, the player will show a DVD as empty when I direct it to look for all files in the D Drive containing the DVD disc. Curiously though, sometimes when I search like this, a warning window appears that says "D Drive is not accessible"

Thank you for any suggestions you can provide.