My recycle bin has emptied itself !

If the Recycle Bin gets too full then future items you attempt to delete would trigger an error message stating the Recycle Bin isn't large enough, asking if you want to bypass the Recycle Bin for these items, permanently deleting them. The only time it would purge older files to make room without prompting you is if someone reduced the maximum size of the Recycle Bin. That, though, requires right-clicking it, going into Properties, and typing in a new size, so it's unlikely to be done by accident. Beyond that the only thing it could be is a third-party program designed to perform cleanup of old files, erase your tracks, etc. Might someone along those lines have been run recently?

John