NXT has 2 "secret switch" in addition to the switch on the front. The one is "reset switch (SW1)". Switch is located on the portion of the arrow in the photograph. That switch is in the pit, then press with a long shaft. Reset function is activated by pressing this switch momentarily. Continue to press the switch for a few seconds (about 5 seconds?), enters the update mode of firmware. In this mode, the LCD will disappear, so will continue to sound like "Putsu, Putsu" from the speaker, please update the firmware by connecting to a PC.

Another switch is to detect the battery (SW2). This switch is an electrical thing; seems to like not detect by the software. The work of this switch is not well understood yet.