That's the common all too often discussed HDMI HDCP HANDSHAKE BLINK ISSUE.

If the usual power off, remove all cables, then pull the power out for 10 minutes then set it all up again doesn't cure it, then it's the fatal issue we all know about. I take no pleasure in these discussions as my feelings about HDCP is like they put flies in my soup and then tell me it's for flavor.
Bob