amp turns off

amp for my sub and a sony one for my speakers and i have a alpine mono and a sony for my speakers and im using a high level imput to connect my rear speakers and everytime i turn them up the amp shuts off like the green light goes to red...does anyone know why that could be?

Wrong impendance, short in the wiring, blown speaker/sub, that should get you started, but theres a few other things that can cause it.