Privacy is privacy no doubt about that , how about to protect your privacy by taking some steps make sure that your PC is not accessible to others.
So you are wanting nobody to see the data in your PC and you are not willing to give permission to others to access your PC.
1.By setting the Bios Password
By setting the Bios password you can make your system not accessible to others,for this restart your computer press Del or F1 depends on the option provided by the BIOS setup your password.Be sure to note it down some where if you enter wrong password three times your PC will not be accessible ,you have to make jumper changes to make the password default.
2.By setting Windows logon Password
You can create users and set them password so that others can not access your Windows.
3.By Locking your PC with Win+L
By locking your PC with Win+L with option provided by Windows to lock your PC which requires your password to give to enter into Windows.
4.Setting a ScreenSaver Password
On the Desktop right Click Properties Click ScreenSaver and give 5min. minimum time to wait and enable on resume password protect.So while you are away away from PC others cannot access your PC with screen saver password restrictions.