There is a total reset procedure for the Denon in the manual.
Hard power cycle (NOT just a standby cycle) while pressing the TWO TOPmost, LEFTmost buttons in the main button array (i.e. NOT the smaller groups of buttons sometimes seen on the unit's face). Works for all Denon AVRs AFAIK. All display elements and indicator lights will blink about once a second. Check carefully to make sure all elements/LEDs are good, then release buttons and unit should boot directly to stereo FM Preset A 87.5MHz at minimum volume (less than -80dB).