Along a similar vein of Win 10 issues—I’ve gotten a few calls regarding Microsoft Office not working after rolling back to Win 7 after a computer upgraded to Win 10.
Something about rolling back to Win7 corrupts Microsoft Office and prevents it from being opened or even uninstalled through normal means.

Microsoft has a tool that’ll uninstall Office.

I’ve attached the tool as well as tossed it up on the network.
“T:UTILITYMicrosoft Office uninstall toolo15ctrremove.diagcab”

1) Run the tool to uninstall
2) Reboot
3) Go to WWW.Office.com/myaccount and have the client login using the account they used to purchase Office.
4) Deactivate Install for the PC you are on.
(Not deactivating bounces an error message and will tell you product activation failed and will pop up everyday letting you know it’s not licensed/registered)

5) Install