-their is a short in the speaker wires.
-the load on the amp is too low (1 Ohm load on a 4 Ohm Min stable amp)
-HEAT
-Subs are going (my rockford 800.2 keep protecting, and after a few weeks of doing it one in a while my sub blew, I guess it was going all along and that was cause the amp to shut off, could be related to #1 or #2 above though)
I am probably missing some, but here is a list to start with.
To check:
1. Double check all the wires, make sure they are nice and neat, and in the correct polarity + to + and - to -
2. Check the Amp's Specs, and make sure that you are not over stressing the amp. Find out what the speaker Impedence is ( 4 Ohm / 2 Ohm). How they are wired (series / Parrallel) Figure out the load on the amp. Example. I have a Dual 4Ohm 12JLW6v2 in series, so my amp see's a 8 Ohm Load). My RF 800.2 is 4 Ohm MIN Stable in mono mode. (Don't ask why its set like this, thats a long explanation) But if I had it set for a 2 Ohm load after long periods my amp overheats since its being stressed.
3. When the amp cuts off, are the amps HOT to the touch?