1999 Pontiac Firebird Trouble Starting

I have a 99 trans am and there are times it won't start. When I turn the key all the dash lights come on, but it won't turn over or start. There are other times it will turn over and try to fire then cut off. And sometimes it does just fine with no problems. I didn't have any trouble until a couple of weeks after installing a sub & amp with the power wire through the grommet in the firewall that has other wires through it. Could there be some loose wires under the glove box?