all of sudden, stereo powers on

2005 Nissan Altima, non-Bose system, kickerkx400.1 amp and one subwoofer, all of sudden, stereo powers on, amp power on, but no sound....can change stations, track on cd, volume up and down, but NO sound, ???? '

amp power direct to 12v battery, ground to chassis, fuses good, power to amp, and to radio, but no sound from any speakers......out of no where the radio would actually have sound, but only for very very short time, then....silience....nothing......