After a set time period I'd like to have my computer lock. I do not want the computer to go into any kind of power saving mode, I'd just like it to lock the screen.
Which setting must I configure?
How about using a blank screensaver?
I assume you already have a password configured for your account.
Open Screen Saver Settings by clicking the Start button Picture of the Start button, and then clicking Control Panel. In the search box, type screen saver, and then click Set screen saver password.
Select the On resume, display logon screen check box, set a time when you want the screen saver to start, and then click OK. (Choose a time that's not long enough for an unauthorized person to use your computer, but not so short that if you stop working at your computer for a moment, the screen saver locks it.)
Source: http://windows.microsoft.com/en-us/windows/windows-password-for-screensaver-password#1TC=windows-7