Did you do a fresh install of windows 10 on the windows 7 partition(s) or did you just do the upgrade?
Are you able to boot windows and Mint?
Are you not able to access the windows data partition Mint? or windows? or neither?
I'd suggest you boot Mint and go to the site below and get the boot repair script and run it. Make sure you select the option to Create BootInfo Summary. This will give details on partitions, UUIDs and the contents of several important files including /etc/fstab.
https://help.ubuntu.com/community/Boot-Repair
