Sound within programme not working

Been using Premier for over a year now, however, upon loading it up tonight,
none of the music tracks I import give any sound, although the programme
recognizes them. Tracks I've used in old projects suddenly don't work and old
projects don't play anything musically. It's as if Premier doesn't know what
sound is anymore.

Incredibly, incredibly frustrating as I have a deadline for a short music based
video and have put aside this week to work on it.

Please help. Or my door WILL be full of holes. : (

Please provide the following details to help us help you:
 <http://ppro.wikia.com/wiki/Troubleshooting>

Cheers
Eddie

Thanks, after hours of working around I found that Premier wasn't assigned to
the right speaker system... it sounds obvious, but the thing is I haven't ever
changed my speakers or any sound settings on this PC, so there is no reason why
they suddenly weren't assigned. And now to top it off my Firewire won't
recognize any of my cameras today, even though it worked yesterday and has done
for years.