Power steering and random misfiring of engine

So I was driving my car today and the power steering went out. so I went and bought some power steering fluid, but it still doesn't work. it works when you're driving the car but when you're sitting still and trying to turn the power steering does not work. Also, my engine is misfiring. I already replaced the spark plugs and I don't know what else I'm going to need to do. I think I'm going to have to replace the sensors, but I do need help with that? you know determining just what I'm going to need to replace or if there's something else I'm going to need to know?