Common to 95% of all audio equiptment is a "Protectiion" feature which turns off the speakers when the electronics or the speakers are in an adverse state, You have only one thing you can do at this point, and that is to check the speaker wiring to see it is not SHORTED, and check the speakers to verify they are all working properly. Other than that, any other cause for the receiver to be in protection is internal and would require technical intervention. Repairs of this nature may run in the area of $75 ~ $150 or more. If you find that your receiver does need service, my advice based on age and development since yours was built would be to replace as technology has superceeded this receiver at a far lower cost than what you paid for this one. I advise you in this manner based on 38 years of audio and video service and I always want the owner to leave the transaction or service smiling, I hope this helps you.
PEACE,
Bri