Smart PC Locker Pro is a commercial security tool which can help to password-protect your PC or laptop, so you can move away from it for a while and be sure that no-one will be able to access your files.
You can, of course, already lock a Windows PC easily enough - just hold down the Windows key and press "L". But Smart PC Locker Pro has additional features which could make it worth adding to your system (especially as the program is portable and requires less than 1MB of drive space).
You're able to have the system automatically lock after it's been idle for a defined period of time, for instance. Custom wallpaper can be displayed when the system is locked. You can choose to have your PC shut down automatically after a specified number of invalid password entries. There's an option to have the program start when your system reboots, and both Task Manager and your optical drives are disabled while the system is locked, making it more difficult for snoopers to find a way in.
Smart PC Locker Pro can also be launched from a hotkey, for ease of use. And an optional Stealth Mode hides the program's system tray icon, so no-one else need ever know it's installed.
There are limits in how much security this kind of tool can provide, of course. If someone starts your system from a bootable disc or USB flash drive then they'll be able to access your drive, and (with the right tools) remove Smart PC Locker Pro. So this is no substitute for, say, full volume encryption, and if someone steals your laptop then the program won't hold them up for long.