I have using Office 2010 with Windows 7 since January of this year. About once a month my pst files simply vanish and are nowhere to be found on my hard drive. My emails, contacts, calendar, etc. are all gone every time.

I thought I could get around the problem by making a backup folder in a different location (on my hard drive) and regularly copying the pst file there. When I got home from work a couple hours ago everything was fine. After dinner when I started up Outlook the file was gone again - including in the copy in the backup folder I had created.

I have deleted and recreated my account a couple times but the problem keeps reoccurring. Can anyone suggest what is happening and how I can stop it?