This is basic I know, but have you tried toggling your video output on the laptop by using the Fn key and F5 (usually) key together? Also, is your TV set to the right input source?
If yes to both of these questions, try a computer monitor on your external video port to see if a monitor will work and to verify output. If a monitor works ok, then the problem has to lay in the TV or cabling.
I tried Fn 1-8 and it didn't work. I used to work fine but now it's not working. Not sure what you mean by my external video. the laptop used to prompt me to change the resolution , but now nothing. nada.