Discuss PGroot's answer to: What should you be cautious about when using System Restore?

If you use System Restore you may be undoing security updates.  That may be what you want, if an update caused problems.  You can run Windows Update to see what updates are due, and install them one at a time so you can find out which one caused trouble. 

Do not turn off System Restore unless you want to lose all your restore points.

Ordinarily you can undo System Restore, but not if you turned it off.