I recently got a used lcd monitor from someone. It had nothing with it to hook up to the computer so I went out and bought what I thought was the right cable for it. HD15m/m is what I got. But when I hooked it up the monitor would keep flickering off and on while it was booting up and when it got to the welcome screen it would just stay black. And when I shut the monitor off then on it would flicker off and on right after that. So I don't know if if I have right kind or not or am I doing something wrong? I made sure it was in tight and everything.