Abstract: A computer system is composed of a CPU, a timer started in response to a power-on and a reset of the computer system, a storage device storing a plurality of BIOS programs, a selector circuit selecting one of the plurality of the BIOS programs, and a system reset circuit. Each of the BIOS programs includes a boot block, and a core block which includes instructions for restarting the timer. The CPU firstly executes the BIOS program selected by the selector circuit. When the timer times out, the selector circuit selects another one of the BIOS programs. The CPU executes the newly selected BIOS program. In the meantime, the system reset circuit developing a system reset signal in response to the timer timing out for allowing the computer system to be reset.