Have you set up "multiple displays"? You should be able to do this by right clicking on your desktop - click on Resolution which should bring you to the screen showing your monitor - you should choose "set up multiple displays" -is your tv screen there?
Try updating your graphics driver
Go to Control Panel Click 'Hardware and Sound' Click 'Device Manager' Click 'Display Adaptor' it should now show your graphics card Right click on your graphics card name and click 'Update Driver'
If that doesn't help do the same again but.... Right click on your graphics card name and click 'Uninstall' Once that finishes - Reboot your pc
On rebooting the standard windows driver will install for your graphics card.