Weird. I don't know what might have caused that, but a system reset might get it back on track (although it'll also erase your settings, so you might want to take a minute to write down stuff like input settings and speaker crossovers, sizes, and calibration). Page 49 of the manual describes how to do a system reset. Basically, turn the unit on, press both MENU and MUTE on the front panel at the same time, and then press 1 on the remote while still holding MENU and MUTE down. Then release MENU and MUTE and wait a few seconds.