You will need to toggle the output on the laptop.

Usually with most laptops, after you have all the physical connections connected and have the tv set to the proper input setting, you would then press a combination on the laptop to toggle the output.

Most HP laptops are either: function(fn) + any key from F4-F7. Check the F1 - F12 keys and check for the key labeled with a monitor. that will be the key you press down with the FN key.