Where should I put the backend MS Access database?
You can try to use third party Access file recovery program to recover your lost and corrupted data from .mdb files. For more details about this software:- http://www.mannatsoftware.com/stellar-phoenix-access-recovery.html
Somewhere on your computer network or local computer that is regularly backed up. You can change the location of your database by logging into Time and Attendance Plus as the administrator and going to the Tools & Options->Options->System Options menu. Just click the Move button to take you through the process of moving the database.