So. I'm using a HDMI cable to extend my display to my TV and it's been working fine upuntill a few days ago, Now it won't display anything. I know my laptop port is fine, it works with a spare Much shorter cable i have. And the cable I orginally used is also fine because it displays through both my PS4 and PS3, I got no clue why It's acting like this and I've never come across a problem like this with any form of hardware, My laptop does not acknowledge my TV with the first cable mentioned either.
HDMI requires that the source - cable - display all meet certain standards in combination. That means that a cable can work with one source and not another. Sometimes a different HDMI input on the TV will work when another doesn't.
You can also try changing the order you boot the laptop and select the input it's connected to on the TV. That also affects the "handshake" that is required for a source and display to recognize each other.