I have never used multiple displays on my PC so I didn't realize I had this problem but, today, I decided to use one of my old monitors that was collecting dust in my room. I plugged it in to the VGA socket in my motherboard, the power came on, but it didn't display anything. I plugged in my primary monitor (normally connected to my AMD R9-280X) to the DVI port on my motherboard to test it; that didn't work either. Could there be a wire that I forgot to plug in? Or anything else that could be causing this problem?