Just make sure it is displaying colors correctly, easily done by looking at something you view regularly on a monitor that displays correctly and make sure they match. Make sure the casing of the monitor isn't chipped or cracked or any visual signs of abuse or taking a fall. Test the different inputs (HDMI, DVI, etc) to make sure they all work.
There isn't much you could do to your rig to improve for $100. You have a decent CPU and GPU that should be able to handle 1080p gaming just fine. I had a 7870 and it is a decent card, newer games may have to have a few settings dropped to medium, but your detail should be fine.