Two things to try:
1) are IN 3/4 and OUT 3/4 connected when the unit is switched off ?
2) Do you get audio if you unplug the cables from IN 3/4 and OUT 3/4 and connect them to each other ?
If the answer to either of these is no, the problem is probably at your end. Otherwise, contact firstname.lastname@example.org and refer them to this post.