I was driving my car and i noticed the lights on the dashboard started flicking on and off and my headlights dimmed. I turned off the headlights and the lights inside stopped flickering. I pulled over and the car was making weird sounds like if it wanted to turn off. I turned on the headlights and it completely turned off. If i instert the key in the ignition the lights inside the car turn on so does the radio but when i try to start the car it makes a noise like if the battery was dead. I just recently changed the alternator and the battery is semi-new. The alternator i believe was from a 2003 kia spectra and it wasn't brand new. I have already took my car to a mechanic he gave it a tune-up but im still having the same problems as i was having before i took it. Yes i am a girl i know very little about cars. Can anyone give me some advice?