Hello,
Thank you for posting your query on Microsoft Community.
I would appreciate if you can provide us the following information to help us understand the issue better:
- Have you made any recent changes on your system prior to this issue?
You may try to run SFC (system file checker) scan from Windows Recovery Environment mode.
a. Insert the Windows installation DVD into the DVD-ROM; Click Exit if the auto-menu pops up.
b. 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.
c. At the command prompt, type the following command, and then press ENTER:
sfc /scannow
Refer this article for more information about SFC scan.
How to use the System File Checker tool to troubleshoot missing or corrupted system files on Windows Vista or on Windows 7
http://support.microsoft.com/kb/929833
Hope this information is helpful. Please do let us know if you need further assistance with Windows, we’ll be glad to assist you.