Are you upgrading to a newer version of Office – Office 2019 ( not the desired version ) or Office 365 and you have an old version of Office on your computer.
After installing the new one uninstall the old version of Office or you may end up with conflict issues.
Just go to the Control Panel and uninstall the old version or use a dedicated uninstall tool like Geek Uninstaller – reboot after uninstalling and you should be fine.