gate

I have a dvr cctv. The video was working but all of a sudden stopped. The dvr is working however when I connect the rca cable to the graphics card to a tv on the dvr there is no picture. If I connect the vga on the same card to a monitor I get picture. I changed the graphics card but still get the same result in that no picture with the rca cable to the tv but I do get a picture with the vga cable to the monitor. Have changed the cable and tv. Any help greatly appreciated.