Screechy Sound, Lights Affected

I have a 1994 Nissan Sentra 1.6, 148000 miles, the oil was just changed about a week ago. My question/concern is that when I start my car it makes a screeching sound, it sounds like its coming from the belt area, so I bought a belt conditioner and it sometimes stops but its over rules it. Well today I am concerned because when I turned on my car as I tried to turn on my headlights it turned off completely with the exception of the headlights which were still on. So I switched the ignition off and turned off the lights and started it over again and the same thing happened. After about the third try it was able to turn on and run fine. Then a little bit later the same thing happened. I want to know if this is something I could fix or if I have to take it to a specific person because I think it might be the alternator but im not sure. Thanks for your help