You may have a virus or malware causing corruption,try to update your anti-virus definitions and run a full system scan. If the issue persists, copy the file "C:\Windows\Logs\CBS\CBS.log" to your document folder (otherwise you can't open it) and open it with notepad. Now search for errors. Which errors do you see?
You will need to repair your installation of Windows 7,You'll need the installation disk to do this . if you don't have one, you'll have to get it from the computer manufacturer. place the disk in the CD tray and restart the computer, then click the "Repair" option.