If you have a large repository the dashboard can take a while to gather all the data. The slowest operation may well be looking for orphans (files seen on disk but not in the database). You can speed this up if you install a couple of plugins and if you know how to set up a cron job. The plugins are available in the downloads here - you need "Restful Plugin" and "Update Remository orphans with cron". Install them in the usual way and enable them. The description for the orphans plugin explains how to use it. Raise a ticket if you are stuck.