Restoring system file in Windows 7
Hello Jorge.
There is this built-in application in Windows 7 (that can also be found on Windows XP and Windows Vista) called System File Checker (commonly abbreviated as SFC).
To run the SFC, please do the following steps:
1. Click on the Start Orb > Accessories and select/highlight Command Prompt.
2. Right-click on the icon and choose "Run as." from the menu that will appear.
3. Input the password for the Administrator account.
4. You will get an administrator  -level Command Prompt window.
5. In the elevated command prompt window, please enter the command: "sfc /scannow" without the quotes
6. SFC will begin scanning and fixing problems as it finds them.
Restoring system file in Windows 7
Hi Jorge Millicent,
You may recover the lost file from windows 7
1. Back up
This may occur where one is using windows back up.
To recover from this make sure the media that was done the back up is available.
Steps
Go to start click control panel
Go to System and Maintenance then back up and restore
Click restore My files and follow the steps in the wizard
2. Restoring from previous version
This occur where one goes to where the computer (Windows) automatically saves
They are also called shadow copies
Steps
Right click file
Click on restore from the previous version
You will see file saved from previous version and the file saved from the back up.
Note:
Before restoring from previous version ensure that it is the version you want by opening the file