When you launch NOAH to the Client Register, All Clients tab, there are no patient records present. Under the Search tab you will find that common field names such as Last Name and First Name are missing.
In this situation the actual data is still in the NOAH database. The field names have been stripped from the database and therefore no data can be displayed. The most common reason for this is corruption in the database; sometimes running Repair on the database will contribute.
Solution
To solve the issue you will need Export the data out of the corrupt database, insert a clean database with field names intact, and Import the database back in.
Export the data to an nha file. Click on File, Client Export, select all the names and export the nha file.
Run a backup of the database using the Database Properties tool. Click on the Tools tab and then Backup.
If the location is using NOAH version 3.5.2, replace the corrupt database using Database Properties, Tools and Replace (after you have done the backup!).
If the location is on an earlier version NOAH, rename the noah.mdb file and reinstall to get a clean database.
Launch NOAH on the clean database and Import the nha file back into the database.
Please remember to regularly run Compact on your database to keep it running in optimal shape.