If you are using iTunes 12.2 or above for PC, the option "Share iTunes Library XML with other applications" must be enabled within iTunes for Tune Sweeper to be able to detect your duplicate tracks.
To enable this option, firstly launch iTunes and select the "Preferences" option that is displayed when clicking the menu icon at the top left corner of the iTunes window.
In the iTunes preferences window, naviagte to the "Advanced" tab. The option to "Share iTunes Library XML with other applications" will be displayed. Enable this option and then click the "OK" button at the bottom of the preferences window to apply the changes.
Once this option has been enabled, relaunch Tune Sweeper and try again.
Tune Sweeper will search for duplicates based upon the search criteria that you have set. If this search criteria is strict, the duplicate search will also be strict and may result in fewer or no duplicates being found. Depeding on what you wish to achieve with Tune Sweeper, it is recommended to use the most relaxed duplicate search criteria possible to achieve the required results.
For instance, enabling the "Album" duplicate search criteria will mean that duplicates of a song that are from different albums will not be displayed. Whereas removing the "Album" duplicate search criteria will recognise those tracks as duplicates.
Note: It is recommended (but not required) that the "Artist" duplicate search criteria is enabled.