[Trisquel-users] How to use line in port to play music from external source

[ollonois]

I want to use the line in port to play music from en external source and use  
my PC speakers as output.
When I connect the device to the line in port, I get no sound output.
Can someone give me an advice, how I have to change my configuration?
I am using Trisquel 9 with Mate desktop. sound card is an onboard Intel HDA