You may want to enable a password for your computer for added security. If you walk away from the computer and forget about it you don't have to worry about somebody going through your personal files. Here's how to do that:

Option one:
If you use sleep or hyphenate mode here is how to do that:

Control Panel -> Power Options > Choose power plan -> (select plan) > Change plan settings -> Change advanced power settings

That will open the Power Options window.

Double click the top entry ie. "High performance" - then double click "Requires a password on wakeup: -> Select YES from drop list

Click the Apply button.
Click the OK button.

Or

Option two:

If you don't want to use the sleep mode option here is the screen saver option:

Right click on the Desktop -> Personalize -> Screen Saver(bottom right of the window)

Make sure to have a screen saver enabled and make sure "On resume, display logon screen" has a check in it and set you wait time in seconds.

You can also do both options for added security.