That's too bad!..Looks like you lost your hive..are you installing
a package?
You might want to invest in a new bottom board, with sound equipment mice can't get in. Same with brood boxes, when put together properly, [flat & square] there is no gap on the bottom board.
I usually wash the bottom board wit hot water, detergent and
a little bleach in spring. Clean out the rest as good as you can...bees will take care of the rest. Dead bees inside cells...don't worry, bees will remove them.

Yep, bought a new bottom board last night and will wash, bleach and sun dry the old one. Save it for some one who needs it or if (big if) I ever start a third hive.

Yes, I lost both hives last winter. It was a brutal winter, but not more than your zone 3, and yours winter over. Even though we insulated and there was honeycomb and syrup, they didn't make it.

I'm determined, so I keep buying new bees....
Marie