How about some more info, what graphics card do you have and what cables are you running to your monitors?
i have an msi twin frozr gtx 760 and have one hdmi (the one that works) and one display port to hdmi as my monitors only have hdmi and my gpu only has one hdmi output, after some more testing it is either the gpu output or the cable that isnt working as if i swap the cables between monitors, it works.