If you are using Office 365, a recent Windows Update updated office to version 2019 which is not compatible with SOLIDWORKS:
Product:SOLIDWORKS Standard 2018
Technically Reviewed Date:9/26/2018
Question:Does SOLIDWORKS® software support the use of the Microsoft® Office 365® software?
Yes and No. The Microsoft® Office 365® software uses the software as a service (SaaS) subscription model. This means that Office 365 includes the most recent versions and updates of Office applications. Because Office 365 is always the latest version of Office applications, there will be periods of time when the SOLIDWORKS software does NOT support Office 365. These periods of time will be temporary, while support for the new versions of Office applications is validated and published on the SOLIDWORKS System Requirements page (https://www.solidworks.com/sw/support/SystemRequirements.html).
As of September 24, 2018, the Office 365 software includes Office 2019 applications. As of this date, no versions of SOLIDWORKS® applications support Office 2019, and you may encounter problems with the various functions that use Excel functionality (design tables, equations, etc.). Support for Office 2019 is planned for a service pack of SOLIDWORKS 2019.