Try this:
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.
Type the following command, and then press ENTER: sfc /scannow (yes there is a space after sfc) The sfc /scannow command scans all protected system files and replaces incorrect versions with correct Microsoft versions.