14. Registry cleaning
The labyrinthine settings file that is the Windows registry can cause errors, program crashes and system restarts if something has gone wrong deep within it. There are plenty of third-party tools that will scan it for problems for you, though not all of them are trustworthy -- Glary Registry Repair is one of the ones you can depend on (though as with any advanced tweaking tool, use at your own risk -- you do back up, right?).
