If its more than a year its almost certain that the account has been deleted which is why when you've logged in its empty - as you've actually set up a new account rather than logging in to your old one.
Dropbox does this to dormant accounts. It does email you numerous times for 4 months before it removes them, and, then after its done it offering a last ditch chance of recovery.
Unfortunately its almost certain your data is not recoverable. However, you can check this with Dropbox direct at www.dropbox.com/support
and then track at http://dropbox.zendesk.com
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