I recently bought a second hand Gigabyte Windforce OC 980. I initially thought it was broken because it just gave me a black screen, my motherboard gave me a red led indicating there was something wrong with the VGA and when pressing the power button, the computer immediately turned off (indicating Windows didn't boot yet). This was the case for two computers i tested it in. I found out however, that when I plug one of my two monitors in through the DVI-D port, suddenly it works perfectly and gives a signal to both displays. When booted up I can even just swap the ports and it will work just fine.
Does anyone have an idea what could be causing this?