Thanks for all of the helpful replies.
have spent several hours on it last night and this morning and found that the audio driver had "disappeared" from the pc. went to Sony and downloaded the original driver, and hey presto, it works.
not sure how the audio driver disappeared, but have just installed sky broadband, so maybe it has done it - who knows what old Murdoch is up to when you click to accept the changes to internet explorer.
will get burning down the original file to DVD, as suggested by Toad, for no otherreason that as backup initially, whilst I then try to play about and do some editing.
again, thanks for the help.
Pete