If you are using Windows 7, right click on an empty space on the desktop and then click on display properties. If it thinks the TV is hooked up, it will show there as 2 displays. If not, it maybe worth while to try another HDMI cable to ensure that the one you have been using isn't defective.
Hi thanks for your reply i am using vista and i tried what you said but still no joy.i also tried another cable. When the cable is connected to the tv and i click on the sound icon on the bottom right of the screen it shows hdmi connection so there is somthing but it's not showing on the tv.thanks again