It is a Harman Kardon AVR75
Page 34 of your manual.
To clear the entire system memory of the
unit, press and hold the MEMO 15 and
CLEAR 16 buttons until CLEAR MEMO
appears in the front panel display.
Release the buttons and note that the
unit will turn off and then on.
Remember that once you have cleared
the memory in this fashion it will be
necessary to re-establish all system
configuration information and tuner
presets.
If the system is still operating incorrectly,
there may have been an electrostatic
discharge or severe AC line interference
that has corrupted the memory or
microprocessor.
If a reset does not solve the problem,
consult an authorized Harman Kardon
service depot.
The memo 15 and clear 16 buttons are on the front panel and not the remote.
Follow that procedure. If it does not work, it will mean you accidentally erased the BIOS from the processor board.
You will then have to ask H K if a service department can reflash it. On a unit that old the answer may well be no.