Before you do a reinstall try one thing. Try "System File Checker". It checks your protected windows files and repairs them if needed.
Right click the Command Prompt and click "Run as Administrator". Type in: sfc /scannow
You might need your Windows 7 DVD so it can get the files it needs. The last time I did it I didn't need it. It's supposed to be able to get the files it needs out of the Windows directory.