Repair Windows 7 system files.

Every once in a while, Microsoft Windows system files will become corrupted and report errors. It can be fix by repairing the files even windows is running, you can still work uninterruptedly.

First click start then type cmd on the search box after that right click cmd select Run as administrator.

On the command console type sfc /scannow, fig 1.1.
It verifies the system files for repair.

If the system had no errors the message would be "Windows Resource Protection did not find any integrity violations."
 But if it finds any errors it sometimes force you to reboot in-order to finish repair the system files.
Goodluck!