I have a 2004 Pontiac Vibe, and I tried to start it this morning to no success. The key fob could not unlock the doors and I have to unlock each door manually to get in. When I did this, I tried to turn over the car but absolutely nothing happened, no lights, no clicking noise, not even the dashboard lit up. I've been having problems with my battery recently and have been meaning to replace it, but nothing like this. Also my serpentine belt was worn down. Is it a problem with my battery and serpentine belt, or something more serious?