This problem can occur because of a architecture problem (32-bit office running on 64-bit windows) or a permissions problem.
The following steps can be used to solve this problem:
1. Navigate to "C:\Windows\SysWOW64"
2. Find "odbcad32.exe", right click on it and do "Run As Administrator"
3. Then continue following the steps listed in the Database Toolbox Guide.
After following the above steps, you will be able to see all the data sources.
