The microprocessor reset (holding input and speakers buttons while powering on)
is really the only step you can take here.
If the problem persists beyond that with nothing connected, it confirms an internal hardware fault, meaning a short in the amplifier output stage or a fault in the power supply circuitry.
Neither is surprising to see on a receiver this age however, as the amp is well past its service life at this point.
It can be fixed, but repairs would be required which will exceed the value of the system. It would cost more ($400 range, on average) to repair it, while you could buy a brand new one with a fresh warranty and updated features for less. I can help you find a repair shop, or recommend replacements if you'd like.
Best regards, ***** ***** for the news,