Tash_dos_mil

I just bought a 2006 Scion tC a couple of months back. The only light on in the dash is what I just figured out is my tire pressure light that I just haven't reset yet. I took it to Midas and they told me I had a bad battery. Ended up buying a new battery and found that the connectors(I think that's what it's called... I know nothing about cars) were all eroded and dirty so the guy cleaned them off and out some gel on it before reconnecting the battery. This was a couple of weeks ago(3weeks max). Recently, my headlights have been weird. One has been dimmer than the other and every once in a while won't work. Tried to start my car tonight and it wouldn't start with the headlights on. I turned the headlights off and the car started but if I tried to turn them on while the car was on, the car would die. Not sure what's going on! Can someone please give me suggestions on what might be wrong?