Our production server was upgraded from Win 7 to the latest Win 10 build last week. There was no issue with OpenVPMS. Windows has essentially left everything as is (thew!) except the Windows Administrator account was hidden by default. A quick googling found a simple solution if logging into that account is needed:

Run command prompt as an administrator, then enter the command:

net user administrator /active:yes

Sign off, then the Administrator account would be available for selection.

Note: I had another user profile with administration rights prior when running Win 7, therefore I could access the command prompt as an administrator above. I'm not sure what would happen if the machine did not have user accounts with administrator privilege. Another work around may be required.