Tip:Check for and Repair Damaged System Files while Windows is Running
If you receive an error message that indicates there is a damaged system file while you are running Windows, try running the command-line utility Sfc. Note that you need an account with administrative privileges (or access to elevated credentials) to do this.
Simply open the Start menu, click All Programs, click Accessories, right-click Command Prompt, and choose Run As Admin¬istrator. Respond to the User Account Control prompt. Then, at the Command Prompt, type sfc /scannow.
The utility will scan your system files and attempt to repair any damage that it finds. Note that it might ask you for the Windows 7 distribution media in order to carry out these repairs.