I had a sony amp do that a couple of years back. I sent it off to be repaired under warrenty and I can't remember what they said was wrong. probably a transistor inside popped.
I was running 8AWG cable back then and even that had a 50A fuse on the battery end.
it's probably not worth spending any money on it. you can get better amps cheap online. 2nd hand stuff is always trading hands on talkaudio.com
I bought a Genesis ST100 for ?100 and it's the best little amp I've had. it's only putting out 2x80w or 1x270w, but it powers everything.