Half of my house drains are backed up. The laundry room sink, the kitchen sink, and a floor drain in the basement. The bathroom sinks, shower, tub and toilets function fine. Where do I start?

You start to snake up stream from the last fixture that backed up. As a rule the best place to snake from the kitchen roof vent but if the cold and snow is too bad you can always pull a fixture and go in from there. Regards, tom