Sharing a PC is never a good idea if you've got sensitive or confidential information that you don't want strangers, or even loved ones, to access.
My favourite way to protect myself is simply to create another profile for other users on my system but this is not always possible if Windows isn't working properly. In which case, one good option is to lock those files and folders that you don't want accessed by prying eyes. System Vault simply can't hide files and folders but it can require users to enter a password before accessing them. It also allows you to remove common files or folders that are accessed from your MRU files on your PC so that anyone using your machine, can't see what you've just been looking at.
One word of warning though - if you install the program, uninstall it and then reinstall it again, your protected files are completely reset. This means that anyone that really wants to access your files merely has to uninstall the program so it's a good idea to use some kind of system protection system in addition to this program. However, the developers advise that to avoid losing your directories and files when re-installing the application in future you should export your list of paths and import them again on reinstallation.
A simple way to protect your files but be warned that it's not very secure any anyone who uninstalls it will have access to your files.