how to scan windows 7 error files to repair errors

Every once in a while the Microsoft Windows system files will become corrupted and report errors. 
The solution to this annoying, but fixable, problem is to repair the files.

first open the CMD
press the Windows key + R

type cmd

2.open cmd

3.type sfc/scannow

4.Press Enter

this trick is supported in few computer systems only on windows 7 os