Same thing happened to me recently, this appears to be a common problem with Onkyo's.
From searching the web it would appear to be a problem with capacitors on the HDMI board.
I've noticed from many posts that Onkyo US and UK are giving out of warranty fixes for this issue, but since I'm in Hong Kong, I've contacted Onkyo and I am they've told me no out of warranty repairs for this issue here.
I'm considering taking it in for repair, but then that money could be better going to a new receiver.
I've also seen video's of people replacing capacitors on their receivers, however that is for a different model.
I've read a couple posts of people baking their HDMI cards and that fixing the issue. So I am considering this before going out and buying a new one.
Anyone else tried this? Supposedly baking capacitors can restore them back to life, so am seriously considering this option before going out to buy a new receiver.