Curiously have you attempted to reboot the SoundTouch 300 and Acoustimass 300 by unplugging the power cord for a full minute, then plugging the sound bar back in? Do you see any LED lights on the SoundTouch 300? If so, which ones are lit and what color are they? Also, how are you connected to the SoundTouch 300, via WiFi (SoundTouch), Bluetooth, HDMI, or Optical?
Let us know the answers to those questions and we can take it from there! Thanks!