Here is what the Knowledgebase/FAQ has to say about this topic:
Problem: What is the name of the file that stores the birds that I've already seen? I need to copy that file to my new computer so I have a record of my sightings.
Solution: All of your sightings are stored in the Database.mdb file. This is a very large Access database file that contains all the information that runs the program. One of the tables in this database includes your personal information such as Sightings, Custom Lists, Hall of Fame records, etc.
You can easily copy this file to a CD or memory stick and then move this file to your new computer. You will typically find this file at C:/Program Files/ThayerBirding/Data/Database.mdb or C:/Program Files/ThayerBirding/eViewer3.9/Database/Database.mdb
To move your sightings data, open the birding program on your new computer. Then click File and then click Import from Previous Version. When it asks for the location of the old data, point it to the CD or the memory stick and select Database.mdb. The program installed on your new computer will then automatically import everything you need from the old database.
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If all else fails, use the Windows search button to find Database.mdb
I guarantee it is there somewhere! Perhaps you installed it on a drive other than the C drive.
Pete