Onkyo TX-SV 727 PROTECT mode
Generally, this happens when there's a loose connection somewhere, either internally, or with the connections. It usually happens when the volume's too loud, and it tries to protect itself.
I'd suggest you unplug everything from it, check all the speaker wires, and then try turning it on, without any devices connected to it.
If it works, turn it off, and reconnect devices, one by one. That should fix it.
If not, it's likely that there's a loose solder inside, and it needs to be sent out for service.