Two things, first, have you tried updating the firmware on your Onkyo. I read that there is a recent update for your model. It didn’t have anything to do with power but you never know. Second, press the Aux button on the side of your 54 remote and then press power. Does pressing the power button turn the Onkyo off and on? If it does then there might be something wrong in the CEC chain. Even though you previously enabled CEC on your devices check each one again to ensure that they are still enabled. If they are, as mentioned, you might replace HDMI cables, one at a time, to see if it remedies your issue.