Dreamcast
Hardware

In-game reset:
Hold L + R + A + B + X + Y and press Start during most games to reset the system.

Delete internal memory settings:
Hold B + X on controller B and turn on the Dreamcast. Release the buttons after the date/time prompt appears. Note: This will not affect your VMU memory and will only reset internal information, such as date, time, and Dreamcast Network settings.

Delete internal memory settings (alternative):
Hold A + B + X + Y and turn on the Dreamcast. Release the buttons after the date/time prompt appears.