RMSe17

Hi, I just had my Promedia 5.1 Ultra system act strange, while I listnened to music, I experienced a loss of sound from all speakers and the sub. I switched the power switch on them to the headphones only, and the sound still came through headphones. After several seconds, I switched them back on, and full sound returned. But them a couple minutes later died again. Does anyone know what is happening? (I bought these only 10 days ago on ebay) Thanks!