Video Card Problems/Third monitor
I have an AMD Radeon graphics card that I've been using to support 2 monitors to my Lenovo pc running Windows 10. Recently bought a third monitor. The card has 3 outputs, DVI, VGA, and HDMI. When I plug in the third monitor, Display in Control Panel finds it, but its in "black". The settings in Display only let two of the monitors work at the same time. They all three work, just not at the same time.
I'm not sure what your question here is - what you've described is typical behavior for most graphics cards (however without a specific model number I cannot say one way or another, although what you're describing *is* very typical, so it isn't surprising). Third (or fourth) monitor support generally requires an additional graphics card, or a graphics card that can support 3 (or more) monitors. However without more information about your PC, it is impossible to suggest an upgrade or replacement part; specifically it is necessary to know what kind of expansion slots the machine has, what kind of power supply it has, the case's form factor, etc. With more information about your hardware and its configuration, and likely some information about budget, I would be able to provide a more directed answer.