Right-click the Start button Windows Start button in Windows 10 (lower-left corner), and select Apps and Features on the pop-up menu. Select the Microsoft Office product you want to repair, and select Modify. Depending if your copy of Office is Click-to-run or MSI-based install, do the following. Click-to-run In How would you like to repair your Office Programs, select Online Repair to make sure everything gets fixed, and then select Repair. (The faster Quick Repair option is also available, but it only detects and then replaces corrupted files.) In Change your installation, select Repair and then click Continue. Follow the instructions on the screen to complete the repair. If that not works take a look on how to fix PowerPoint files here.