Can't play any type of sound!

Hello I’m making an IDE for making games with lua scripting…
but my problem is very easy and stupid!
I can’t play any sound in mono game!
I’ve tryed: .mp3, .mwa and also builded the sound with the MonoGame Content Pipeline Tool (.xnb) (I’m 100% sure that the files were in the content folder!)
and I’m using MonoGame 3.4 on Windows 10 with visual studio 2015, .net framework 4.0

in load content I do:

song= Content.Load<Song>( "mymusic" );
MediaPlayer.Play( song );

no error is given! the game is simple muted (but it draws the game…)

please help me in some way! (please note that the game must run on all platforms)
also a working example (with source code) will be ok!
Thanks in advance!