This probably means your light isn’t pointing at the layers in question, although you haven’t really given us enough information to know. What kind of light is it? If it’s a spot light, you need to point it directly at the surface of a 3D layer – you can set the light’s point of interest by twirling down the light’s ‘transform’ options. Copy one of your layers’ position properties and paste them into the light’s point of interest and see what happens. If nothing, post back with some more information (light type, intensity, screenshots).
If you don’t want everything to go black when you create the first light, make it a low-ish ambient light, which will evenly light the whole scene. Then you can pick out areas with spot / point / parallel lights.
Also, you’ll find lighting a lot simpler if you follow some basic tutorials first, or at least read the help page:
https://help.adobe.com/en_US/aftereffects/cs/using/WS3878526689cb91655866c1103906c6dea-7e29a.html
I’m not sure there’s actually a problem here – to be honest, everything going black in the scene is exactly what should happen, unless the new light is ambient or happens to be pointing at something in the scene.