1. A computer implemented method of controlling access to a computer system, said method comprising the steps of: said computer system operating in a fully operational mode in which an operating system in said computer system is operating and said computer system executes one or more user applications installed in said computer system; in response to a predefined time interval lapsing, said computer system automatically switching the computer system from said fully operational mode to a limited operational mode in which said one or more user applications are automatically terminated, said operating system is automatically shut down, and a BIOS within said computer system automatically solicits entry of a password by a user, and if said user fails to enter a valid password, said computer system preventing operation of said operating system and execution of said one or more user applications.