The LED on the unit itself is the SAG control which won't light up if the knob is all the way turn down.
Are the LEDs in the modules lighting up? if not, then obviously the unit is not working properly or even getting any power, the problem can be anything from a bad power cable to a blown fuse or some component fried inside.
Try troubleshooting: plug the unit into another outlet, use a different power cable, check the fuses, change the input tube (which you already did), use a different module to discard a malfunctioning module.
If you still can't get it to work, you should contact Synergy directly, I'm sure they will help.
On issue I had was that my unit powered up but there was no sound at all, when I sent it for repair, Synergy told me that there was an internal issue that made a fuse blow, they fixed the issue and I haven't had another problem. Apparently it's a documented issue that some people have had.