Thanks for responding.
I've set the jumpers so that the benq is the master (as was the cdrw it replaced) and re-checked that the oem dvd is set as the slave which it is. The only software installed recently is what came with the benq drive ie. nero and qsuite. I've been 'messing around, opening with various programs and strangely, although there is no audio with windows media player, real player, musicmatch jukebox or nero showtime, oddly power dvd works!!
I've also noticed that when I insert a disc into the benq drive (audio or dvd), it takes an age for the applet asking what I want to do to appear and my cpu, which is 2 ghz screams up to 100% effectively temporarily freezing everthing else.
Not sure what to try next other than reinstall the software!
Any alternative suggestions?