iTunes now no sound? but has artwork

I have the latest iTunes version.

My music files are listed and the display shows the moving bar as they play.

However I can't hear anything from my iMac.

This is a screen shot of the list. Duplicates appeared when I downloaded iTunes again to see if that would cure it.

If I get into a specific file to check the location then this is what it tells me -

The location in iTunes preferences looks ok to me -

I have home movies stored on an external drive and they play fine, including the sound.

I'm guessing that somehow I've messed up a link.

Can anyone help please?