It should be under /users/%yourusername%/appdata/roaming/leafcoin
As long as you aren't already using the windows wallet.dat you can replace it with your other back up.
You may need to enable hidden folders under the "view" setting to be able to see "AppData"
wallet.dat corrupt.
it needs the android app to load cuz i had this issue with infinitecoin and i was able to get my coins with infinitecoin android wallet from playstore