Keep getting "overload" error message in display?

Hi,
I have the Technics SA-AX 730 receiver, and up until very recently it had been working without a problem. When I now try to turn it on, it will display the usual radio station, etc. for a few seconds, before switching to the "overload-switch off" error message in the display. I've replaced all the speaker wire, and have double checked the speakers impedance. I've tried turning it off, unplugging it, as well as the "help/reset" button, etc, but no luck. And to be honest, that's pretty much the extent of my "electronic repair" knowledge. I would sincerely appreciate any insight or help you can provide with this problem, and thank you in advance for your time and help in this matter. Have a very good day, L