4 gauge is too small to begin with for that amp anyways. However, that is not likely the reason your amp is shutting off. If you have a DMM (digital multimeter) or voltmeter can you measure the voltage at the amp?
There are many reasons but one possibility is the way you have your sub(s) wired. What sub(s) do you have and how are they wired? It could be that the load on the amp is too low and your amp is going into protect mode.
Is your amp going into protect mode or simply turning off? If it is going into protect mode then there is going to be troubleshooting in the manual that came with your amp.
There are so many reasons that you could be having this problem. It is hard to say for certain without more information.
Good Luck!!!