Hello,
If you open the program and you go to ¨Options¨ then the ¨Metronome¨ tab here you should see the Metronome volume bar, make sure that is turn all the way up. Then under the ¨General¨ tab make sure the correct playback device has been selected.
If this is all setup correctly then I would suggest you try reinstalling the program without uninstalling so you do not have to register again. If that does not work, then you should probably create a support ticket for NCH Software Technical Support, you can do so from this link: https://www.nch.com.au/support/index.html 
Good Luck!