90q 20v starter problem

Hey all, just got my sound system put in, but now the car won't start. When I tried to go home, the starter turned over once and then nothing. Is there any wires I shouldn't have cut in there. It think it's kind of funny that the starter started very good for that long and now nothing won't even click.

have you wired the audio system to permanent live if the amp "if fitted" is on all the time it will drain the battery pretty quick which I think is the problem but im no expert in fitting audio equipment, flat battery I think