Seems like your hdmi driver got messed up or something.
Try using a external screen and plug it in, if it works then check your hdmi drivers and reinstall it.
But if you don't have a external screen try the following:
1. Try booting up your PC/Laptop with the HDMI cable connected to a TV that is on.
2. You can try booting up the PC/Laptop while the TV is off and then turn on the TV.
3. If the above options don't work, try booting up the PC/Laptop first, and, with the TV on, connect the HDMI cable to both the PC/Laptop and TV.