No Sound

I suddenly seem to be having problems with my CD/DVD drive. I have an internal CD/DVD drive and an external one, but neither of them are playing any sound when I put DVD's in them. The speakers are working, as other programmes and system sounds are working fine, but not the DVD drives. In fact, the external drive doesn't even seem to recognise when a disk is inserted!

Can anyone give me any advice? Our anti-virus caught an incoming trojan on Friday - could this be anything to do with it? Have tried system restore, even going back to the end of November, but it keeps telling me that no changes have been made to the system!