Two things to look at.
1) make sure you understand how the routing works. It's entirely possible to get no signal if this is set wrong. A check is that if it works when bypassed, but not otherwise, you probably have a routing issue.
2) If you are going from XLR to jack, make sure that all pins of the XLR are connected.
If you have not already, try returning the unit to factory defaults (hold down 8 at second powerup screen).
