First of all you should check the signal path of your mixer from gain through Fat Channel to fader to routing (mains) to fader to master fader to see if there is signal coming in and going somewhere. If you see signal in the master output and the fader is raised and there is no sound, check the volume knob on the front of your mixer, if it is turned up (fully). You can also make this test with the mono mains. Also cables could be checked, but probably there is nothing wrong.
If this does not help to get the mixer going, I would recommend a factory reset with the option card pulled out. This will renew EVERYTHING inside your mixer, but you will also lose all your settings. You should save scenes and presets to your computer first. The factory reset can also be used as firmware upgrade, but this is not a must. You can also use the firmware version which is installed now, if it fits to into your studio surrounding. Most important is to use matching versions of firmware and software, so check the download page and the information in your PreSonus account. In your account you will find detailed information how to do upgrades and resets.
This is the download page for your mixer: http://www.presonus.com/support/downloads/StudioLive-RM16AI.
