Type command prompt in Start menu search box and then hit Ctrl + Shift + Enter to launch the Command Prompt with administrator rights. Alternatively, go to Start, All Programs, Accessories, right-click on Command Prompt and then select Run as administrator option.
Click Yes if you are prompted with UAC (User Account Control) box.
Once the Command Prompt opened, type sfc /scannow and hit enter. This command scans integrity of protected system files and then repairs if problems found.
The process may take a few minutes. Once done you are good to close the Command Prompt.
You can also type just sfc in the Command Prompt to know more about sfc commands.