Could be a couple of things going wrong. could have overheated and shutdown to protect it. could have hand to many incoming wattage/voltage from your head unit and shutdown. could be that the ohms rating on your speakers is to low or that the speakers could have heated up and bumped the guilds and caused it to shutdown. don't know if you know how ohms works. but here is an exp. if you have and have that is rated at 4 ohm stable and that is the lostes ohm recomened for it. and you have two 4 ohm rated subs. you can run them and run them with no problem as long as you don't bridge them. run them off of the same port on the amp. when bridging them it devides the ohms in half. so 2 4ohms would become 2 ohm. 2 8ohm would become 4 ohm etc. if you are running 4 speakers in pair that are 8 ohm each the total together would be 2ohm. hope this helps. try to duplacate the conditions that was going the other day when it shut down same bass settings same song etc and see if it happens again if so try unhooking one of the speakers and try it again if it don't do it it was overloading it if it was overloading and you know its right ohms etc. send it in sorry this is so long.