How to Protect Your PC from unauthorized access When Your are not using your PC??

When You are not using your PC or you are not near to Your PC and you don't want to Turn Off your PC, Then Simply Press Windows key + L to lock your PC. Now You are free from the worry of unauthorized access to your PC.

for more, Use Windows Event viewer to investigate unauthorized access to your PC.
To open up Windows Event viewer, press Windows key + X, and then select Event Viewer from this list.