Need help w/ my 2002 C-230 Kompressor.

I have a 2002 C-230 Kompressor and lately it has been draining my battery if i don't drive it every day. So i bought a new battery thinking it was my old battery that had the problem and now once i put the new battery on and the lights came on but the car wont start when i turn the key, and it makes no noise. Not sure whats causing this but my neighbor says it could be the alternator, ignition or voltage regulator?


