I have done just about everything. Powered the tv, changed the HDMI input into the tv, powered off the roku changed from 720p to 1080p and I have a 1080 tv. At this point I can let my son play angry birds but that was not the soul purpose of the roku. I can select the show from the channel and I see it loading, but as soon as the video starts the screen turns purple. I am a little dissatisfied with the product if I have to do so much to get it to work and I have only had it for 3 months.
When you "Powered the tv" did you unplug it? The power switch on most TVs don't actually power every thing down and fully reset the processor in them.
What you are describing seems to be the result of HDCP (content protection) hand shaking breaking between the Roku and the TV. The Roku will fully restart it's side of the process on an HDMI unplug/replug operation and, of course, when it is power cycled. But if the TV's processor is out to lunch that will be of no avail. Since your combination worked earlier I think the most likely thing is the your TV is acting up and the "power switch" on the TV is unlikely to fix that but pulling the power cord might well do it.