HD TV as a monitor

I have the DVI computer output converted to HDMI, the HDMI cable connected to the HDTV, but my computer does not recognise the TV as second monitor. What am I doing wrong, or what else do I need to do?

well, is it showing up with a duplicated image? cuz if so just go into ur graphics properties in windows, for xp right click desktop and click properties and go to the tap for the monitors/resolution, in vista go to personalize and i think displace settings, and windows 7 right click desktop and select screen resolution. once there u should be able to do something in order to chose to duplicate the image or not, im not sure but i think u jsut put a check in a box and click apply, but im in windows 7, and its a bit different here, and i don't have a second monitor, so i cant say for sure

If you have an ati card, the catalyst cenetr has an option for setting up monitors (cant remember name you'll see...) nvidia has the contol panel wih the "set up multiple displays" if that dont work, try using the Tv as the primary display ...