Obviously your initial connection is lost.
Not knowing which versions of Excel & Access you are using – here are my comments on Access 2007 & Excel 2007. You may try to re-connect the fields from access database (Of course this assumes you know the table name or the query name!).
Click on the Excel cell that you want the data from access-db, click Data, then From Access (top left hand side), select the database, then select the table (or the query); on Import data screen – select Pivot Table Report & then Ok. Hopefully this will populate the needed data.
You may experiment with the property field & make it “refresh data when opening the file” or “Remove data from external data source before saving the workbook”.