When you click on the Windows 10 hard drive in Files, you receive an error message stating the operating system was not shut down properly and cannot be mounted.  The error message will list the hard drive device, normally something like /dev/sda1.  Make a note of the device location.  These instructions assume your device is located ad /dev/sda1, so adjust accordingly.  Open a terminal window and create a directory to mount your drive.  The following command will create a directory in the root of the Linux files system:

mkdir /temp

Mount your Windows hard drive into the temp directory with the following command:

mount /dev/sda1 /temp -r

This will mount the drive to the temp directory in a read-only state.  You should now be able to access files on the drive through either the terminal or the Files program from the desktop.

A possible fix to this issue is to use the Windows shutdown command at the command line to turn off the computer instead of shutting down through the GUI.  The command to shut down Windows is:

shutdown /s /t 0