I can’t be too sure but I think this may have been due to the new Xbox 360 update.
By accident Microsoft have botched the HDCP with the new patch. It’s also been affecting quite a few people with certain HDTVs.
All I can suggest is wait until Microsoft brings out the console patch (coming soon), use Component cables or get a HDCP stripper.
Also check in the Xbox 360 settings to see if Display Discovery is disabled. Sometimes when it’s on it will produce no picture through the Intensity Pro.