After 360 reinstall, online backup not recognized

I had to reinstall N360 when errors could not be fixed following a XP restore to earlier date.  Programs all work properly.  Version is 5xxxx, the latest.  I was asked to do online backup.  Previous backup online contains documents and settings but no photos.  A totally new backup set was made instead of recognizing the previous online backup.  Why?  XP media version, IE 7.  I would appreciate an answer to what happened and how to avoid using  up expensive backup space.