Help with my HDMI cable connected to my series 5 Samsung plasma TV from my xbox 360?

Every time I connect my HDMI cable from my Xbox 360 to my series 5 Samsung plasma TV it says "Check Connection Signal". It is connected to HDMI port 3 and I can't connect it to any other HDMI ports cause they are occupied by the cable box and blue ray player. I have tried connecting 2 other HDMI cables and they didn't work either. Please help, thank you.