If you see a blue or green screen, try this: 

On both your Roku player and your TV or receiver, unplug each end of the connectors and plug them back in again, pushing them firmly, all the way in. Try viewing the video again. Sometimes, the blue or green screens are the result of a loose connector.

If you continue to see only a blue or green screen, your TV or receiver may not support HDCP (a content copy-protection solution) over HDMI. This is generally true for older TV models that have early HDMI implementations that do not follow current standards.