Probably a system file problem.
"Simply open the Start menu, click All Programs, click Accessories, right-click Command Prompt, and choose Run As Administrator. 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."