Protecting Individual folders.

I have alocal PC being shared by four users.The PC is not connected to the network. each user is from a different department and does not want his data to be seen/accessed by the other users. How do i protect each users’ folder?
Recently, one of myusers lost a folder in the PC, either it was deleted maliciously or accidentaly by his collegues sharing this Pc. How do i stop this?