Follow the directions below to reset your Apollo 16/16 mkII hardware:
1. Shut down the Apollo 16 and computer.
2. Disconnect any cables connected to the Apollo 16 except the power cable. (this includes disconnecting the FireWire / Thunderbolt cable). If there are any monitor speakers or headphones connected to the Apollo 16, make sure that they are either disconnected or powered off before continuing.
3. While the Apollo 16 is powered off press the two buttons on the face of the Apollo 16 - the Meter button on the left side of the display, and the Monitor knob on the right side of the display (see picture below for reference).
4. Keeping the buttons pressed down, turn on the power switch to the Apollo 16 - hold down the knob/button combo for approximately 10 seconds until all LEDs on the front of the Apollo 16 remain lit. Once all LEDs on the front panel of the Apollo 16 are lit you can release the two buttons and shut the Apollo 16 down once more - note that the LEDs will stay lit until the unit is shut down.
5. Reconnect all cabling and power up the system like normal (it is recommended to always turn the Apollo on before turning the computer on).