3 monitors connected to PC, won't allow use of all 3

Hi all,

So my problem is my computer recognizes that I have three monitors connected but when I try to utilize all three it only uses two. All of the monitors are different brands but I didn't think that should be the issue. The computer works fine and so does the monitor itself. The only way it allows me to use all 3 is if I duplicate one of my screens but I only want to extend the desktop. I've tried everything I can think of to fix this problem.

Help please?