This is because older HD-ready TVs are not HDCP (High-bandwidth Digital Content Protection) compliant. HDCP-compliant devices were released on the market in 2008 so any flatscreen TV purchased before then is likely to have problems with newer HD equipment.
Sometimes, although thankfully it’s quite rare, an HDCP device and non-HDCP device will not talk to each other at all and it will not be possible to get a picture to show on the TV. Often, however, the HDCP device is configured to only show non-HD video to non-HDCP TVs.
What this means is that if you buy a BluRay player or get SkyHD for your pre-2008 flatscreen TV you won’t really be enjoying true HD content but just plain, old standard definition content.
There are three solutions to this problem – either a new TV, a device called an HDCP stripper or a device that converts the HDMI to a non-HDCP connection such as component video. Neither the new TV or the HDCP stripper are cheap options but converting the HDMI signal can be achieved for about £75 by using an HDFury. The only requirement is that your TV has component video inputs.