make sure your tv input is set to the HDMI port while you do this so that it can send the signal. When i first used HDMI on my laptop it didnt work but when i changed the tv input first, my laptop showed me some options for dual screens. If you already did this, go to control panel, adjust screen resolution, and click on the second screen, then click extend the desktop onto this monitor. If this doesnt work then you might have a faulty cable.