Here's a good way to lock down window without Hiding the Screen
KeyFreeze – http://keyfreeze.com A freeware useful application to lock your keyboard and mouse in order to avoid others from messing up with your computers.
Its a common situation for small children often play with key board and mouse and result in unwanted command in your computer. In this case, you can just have your keyboard and mouse lock/freeze using KeyFreeze.
The application is easy with simple Ctrl+Alt+Del –> Esc command