My laptop won't connect to my tv?

i have an HP laptop and it used to connect fine to my TV but sometimes it doesn't work and i don't know how or why but now it won't work. I have an HDMI cable i use and whenever i put the HDMI cable into my laptop the TV screen goes black and my laptop does too. I hit fn + f4 which is a projector button and it gives me options and i tell it to duplicate the image on my laptop to the TV but it doesnt work the TV remains black. please help because i would like to watch movies on my TV