It works much like Safe Mode in Windows. The program’s software starts in its most basic configuration, with no frills and glitzy features, to simplify troubleshooting. You can then hopefully identify what is causing your problems.
Troubleshooting Office problems is never fun, but Safe Mode can help you find the cause of errors a little faster, so you can get the actual work done. This is how it works. Once you know the trick, it’s easy to remember.

1.Hold down Ctrlkey when you double-click Officeshortcut or click the program on the Start menu.
2. Say yes to the dialog box that appears and the program will start without any add-ons and without any customization you have added yourself. If it works fine, you know one of these add-ons or your customization is causing the error.
3. There is another way to do it if you want. Type the name of your program in the box Drive (in Windows 10 you can find it if you right-click the Start button) and add /safe after. In other words word/safe, excel /safe or powerpnt” /safe.