If you can't play audio files with rekordbox for Mac/Windows, check if the following applies:

The file format is one that's not supported by rekordbox.

Only certain applications can play the audio file, e.g. the audio file was downloaded from Apple Music, etc.

The location of the audio file has changed.

The audio file is damaged.

For details, see [Management] and [File formats that can be loaded and played] in the rekordbox Instruction Manual.

You can read the rekordbox Instruction Manual [rekordbox.com].