Car will not start

I was over at my friends house and we were installing his subs and amp into his car. When we got all of it in the car his car wouldnt start. When he tried to start it everything would work and lights would blink. When he tried to start it it was clicking and i had thought his battery was dead. But everything was still on so it couldnt have been that. Any Ideas?

Hey man make sure that you have a good ground. How big is this amp the subs? You may have to get another battery or a bigger alternator. But check all the wiring first. Then you should look into a bigger battery and alternator etc...