2005 Buick La Crosse Possible Electrical

This morning driving our son to school, the heat/fan would not go on - could not defrost windows. When my husband hit a bump - everything bumped on. This also happened with the headlights a few weeks ago - I was driving at night going 55 mph on the road and all the lights inside/outside the car turned off (thank goodness I had the fog lights to turn on). I did not test the brights. Then a couple of miles later down the road, the lights came back on.

Any ideas as to the problem? Estimated cost to fix?