How to fix the *Digital Input Self Test Feature Check*

I just got this monitor from a friend of mine, and i think it's a 2007 model with no spots to plug a USB Cable or something which means I can't use a mouse or keyboard, I also don't have a CPU or the big box thing that I think goes with a monitor. And so I just plug on the monitor and the first thing that pops up on the screen was the Digital Input Self Test Feature Check, with the colors Red,Green,Blue, and White on it. Please can you tell me what is the issue here and how do I solve it. Do I need to get a CPU or something else?. Please kindly assist me on resolving the issue.