99' Monte Carlo Won't Start

I have a 1999 Monte Carlo Z34. About a month ago my car kept dying and I kept having to jump it, so we figured it was the battery and replaced it. About a day later I had the same problem, even with the new battery (it wouldn't even try to start) so my dad thought it was the alternator and so we got a BRAND NEW one and replaced that, it seemed to work for about a day and I went to use it today and it wouldn't start. I was driving down the road and today and it just totally shut off while I was driving. Now I went outside and the brake lights were flashing on and off, when I opened the door the lights started flashing on and off, so I tried to start it and it started buzzing and acting crazy. PLEASE HELP!