Try connecting the unit with the AV cable (yellow composite) and connecting to that input. You don't need to unplug the HDMI cable - both can be connected at the same time.
If you're able to get to the menu in the Blu-Ray player on the AV input, go into the menu and increase the resolution. Then switch back to the HDMI connection to see if you're able to see the picture. It may be that the resolution may have defaulted back to a lower resolution.
Does that help?
My BD-C5500 has suddenly stopped working. When you power on, you get the Samsung background screen, but then it goes to black. It does the same thing whether there's a disc in or not. I have tried to get it to respond, and sometimes it will light up STOP or something, but the screen never moves from black.