I used my Windows Live Mail as usual in the morning then had a meeting so switched the PC off.  When I turned the PC on two hours later and ran Windows Live Mail my Inbox and all the subfolders were empty!  I had not deleted anything and, indeed, if I had physically deleted all the items it would have taken an extremely long time to do so.  This was not the case.  The only thing that happened was that as I 'Shut Down' the PC the message 'Recovering unused disk space' came up which happens every few weeks.  I think that during this process the emails are saved to a temporary file until the recovery is complete but, on this day, the PC shut down before the emails were 'restored'.