ur battery is dead, or your battery cant deliver the power the sub/amp is trying to take. try 2 batteries, or giving the battery more charge with a better alt or sumthin
Could be you put your speaker ohms lower than your amp can handle!! EX:your setting is 2 ohms but your amp can handle only 4 ohms!!! THATS WAT HAPPEN TO ME!!
what kind of amp do you have cause most likely the alt cant handle the power and the amp senses the clipping and shuts it self off to prevent any further damage