1. Click on start then run
2. Type in sfc.exe. You will see the
following window

3. Click on settings as shown by the
red circle below.
4. Check off both Check for changed
files and Check for deleted files as shown in the red circle below.

5. Click OK
6. Click Start and you will get a
window that looks like the one below.

7. If you receive a prompt on
changed or deleted files choose update on all files (as shown in the
graphic below). The graphic below is for changed file, but deleted
file is similar. I just ran a system file check and I didn't get any
deleted files so couldn't give screenshot of it.

8. If you receive a notification
that a file is corrupt you will want to restore this file, unless it
is a setup file which is associated with some of the versions of IE,
just choose update for this one if you get it. The one shown in the
graphic below is a setup file for IE and I get this message every time
on any machine after installing IE.
9. When system file checker is done
you will most likely find that your computer is performing much better
than it was before. Screenshot below shows the result of a scan I did.