How do i know if an amp is blown?

I have 2 kicker comp vr 12" subs and a 1200 Watt pyramid amp with 4 channels. 1 of the channels already didnt work and i noticed a resistor inside the amp was broken but half of the amp still worked fine. I was driven one day and my subs just stop hitting. I didnt see any blown fuses and the amp still says its getting power but my subs are silent. Is my amp blown? and if not how do i fix this