You can lock you desktop when you are away with a simple shortcut to avoid any kind of misuse of your PC. I know this is an old one, but this is meant for those readers who don't know it, so don't flame against this topic. lol
There are two ways to lock your desktop when you are away:
1. Press and hold "Windows" key on your keyboard and press "L".
OR (For Those Who Don't Have The Windows Key)
2. Create a shortcut on your desktop with the following path:
3. You will get a screen like this, with your user account (you need to password protect your user account for complete protection).
Bravo!!! You are done.