Some Siemens' cooktops -- cooktop-only models or oven/range models with attached cooktops -- have a control panel lock that you can turn on to prevent use of the stovetop burners and control panel. This lock is set using the control panel or, on some models, with the removal of a magnetic temperature dial that locks the burners if it is removed from the cooktop. Siemens designed the cooktop lock feature to prevent injury while cleaning or to children trying to use the stove without permission.
Press the "Panel Lock" or "Cooking Mode" key on the control panel for at least five seconds. If your cooktop has a "magTron" dial that you removed when you locked the cooktop, return the dial to its original position and then press the "Panel Lock" button for several seconds.
Turn on a stovetop burner to confirm that you've successfully unlocked the stovetop.
Flip the circuit breaker switch for your Siemens' cooktop, oven or range to power off the appliance completely and reboot the control panel if you still can't use the stovetop. Flip the switch, reset the clock and then turn on a burner.