Sounds like overload protection is kicking in. Where on the scale does 15 fall? Is it a dB scale, or 0-100? The K120 speakers only need 10-80 watts to operate and shouldn't be loading that amp too much with just the 2 units, but if you have a full surround setup you have to pay more attention to power requirements and speaker loads. The spec for your receiver is 100w per channel into 6 ohms with 2 channels driven and your speakers are 8 ohms. If you don't have any other speakers connected and it is in fact an overload fault, then the speaker(s) might have a short in the coil (or there could be a short somewhere else so double check your wiring). It could also be shutting down erroneously (IE: no short or overload, but still shuts...