Open an elevated command prompt.
To do this, click Start, click All Programs, click Accessories, right-click Command Prompt, and then click Run as administrator. If you are prompted for an administrator password or for a confirmation, type the password, or click Allow.
At the command prompt, type the following command, and then press ENTER:
The sfc /scannow command scans all protected system files and replaces incorrect versions with correct Microsoft versions.