I am talking about that setting in your list 
Activate the Metering mode, and switch it from “Auto Exposure Histogram” to “Manual”, then activate the Exposure Compensation, and move the slider until your scene looks right.
Hint, for me, sometimes it´s jammend and those settings and sliders won´t react. If that happens to you too, then go into the project settings and search for auto exposure and turn it off there too, then those settings and sliders should work again (maybe a restart might be necessary).
However, i have the feeling, that you have one particular light in your scene, which is so extreme powerful, that other normal lights are way to weak in comparsion to have any impact on that scene, and your now completely white scene seem to confirm that ^.^ You mentioned, that you have a SunSky imported. Those contain a directional light, which usually act as the sun, with sunlike settings for their brightness, intensity 75000, if i am not mistaken. Just for comparsion, a regular light that you bring into your scene is usually set to 8 or 10 
So what probably happened in your scene, your auto exposure is adapting to your way to intense directional light from the SunSky actor (because its a literal sun), making it impossible for all your normal point lights etc. to have any noticeable impact. So you should first reduce that SunSky directional lights intensity to match it with the other lights (or turn it completely off for testruns).