All subs will not work?

I have 3 alpine type r 12's and 3 mrp-m500 alpine amps every thing is hooked up right and all the blue lights come on like always but now i have no b only my regular speakers are working. I was driving and had my subs playing and i went to the store when i came back to get into my car to drive back home my subs where not working everything is hooked up the same as always wat could be the problem 10 points please help. and i also checkbehind the radio and uphook all subs and amps and rehooked them up and they are still not working what happen?