Many thanks for the replies above, and massive apologies for lateness in responding - it appears that my frustrations did not mix well with whisky and I needed a new laptop after that night. This I now have, but christened it with (hushed tones) Neverwinter Nights. On returning to BG I now find that it won't play at all. Time for a full reload. Deep joy.
Anyway, my thanks again. Who knows, maybe the re-installation will correct the glitch.