How to make my second screen not be blank.?

My second screen is a TV. My monitor won't pick my TV. It is a SAMSUNG sync master. When I am in control panel it only comes up as display on vga. I have already used the HDMI socket in my TV so I can’t connect a dvi socket from my computer to the hdmi socket in my TV. When the TV is on its own it works fine with the computer however when both the TV and monitor are connected at the same time the TV is blank. The monitor is connected to the main vga socket. There is no signal This is the same with the monitor. When the TV is plugged in to the main vga socket the monitor is blank. I don't know how to re-tune my TV on top of that.