In Feb/March they appear dead, but they are just motionless-frozen, but still alive. Case in point. I had a nuc this spring that I thought had been frozen out, all the bees looked black like they had been rotting for awhile. So I rummaged through and found the queen and was looking at her. I had her in my hand and was looking around at other things, then she started to move. Her color came back and I caged her and made a new nuc. As of now, I've gotten 2 splits and 2 swarms from that one queen, so don't write off the bees OR open the boxes until late spring.
What else...
I put my hives in groups and use insulated tops. I use sheep wool as my insulation and it works great. Don't give them too much room in the winter. It's tempting to leave an extra box of honey on, but that will just be more area to loose heat.