A hardware and software controlled on/off circuit for computers is provided. The on/off circuit comprises a control circuit which produces first and second signals, wherein the first signal causes the computer to execute a software program which prepares the computer for power removal and which returns a third signal to the circuit when the software program has prepared the computer for power removal, and wherein the circuit produces the second signal to disconnect the power supply in response to the third signal. If for some reason the software program should "lock-up" the computer, the on/off circuit and provides the second signal to disconnect the power supply if the software program has not sent the third signal after a predetermined time from when the control circuit sent the first signal to the software program so that the computer may be shut down.