Sound options on my computer (which you can access in your control panel) then set your sound default as HDMI, just remember to set the default back to the laptops speakers when you are finished using it on your TV.
Win+P (DisplaySwitch) -> Computer only = Laptop
Win+P (DisplaySwitch) -> Projector only = TV
(If it fails to display picture on both, press Win+P again, Left Arrow once, Enter. Repeat until it does.)