It is an I5-8400 processor, Motherboard AsRock H310M-HDV/M2, windows 10 pro 10.0.18363 build 18363. I have one connected hdmi, one vga, and one dvi. All three monitors work I can use any two of them but I can't get the third to extend or enable. I can switch which two I am viewing at any time so I don't believe it is a cable problem. From what I have read the graphics card supports 3 monitors.
Your processor supports three monitors:
How AsRock implement support for monitors on their board is a question you have to ask them.