Two computers + Two monitors HELP

[GM Rod]

Alright gentlemen.
To make matters simple, here's a graphic to show my setup:

 

So here's my problem:

I can't seem to get an image from the Mac to display on the ASUS monitor.

The Mac only has one HDMI port. But it also has 6 thunderbolt ports which can also accept miniDisplayPort connections and will work with monitors.

The PC has a GTX 1080Ti with 2+ DisplayPort outputs.

 

Now, I've connected this mac to this ASUS monitor in two ways:

- MiniDisplayPort to HDMI adapter (SEE IT HERE)

- MiniDisplayPort to Displayport cable

 

Both ways worked when I was using the ASUS monitor as a single display for the mac.

And then I added the LG, as per the connections in my diagram and it STILL worked.

Until yesterday.

 

For some reason, now I can't get the ASUS to show an image from the Mac unless I use the ASUS' DisplayPort port.

HDMI just doesn't wanna work anymore.

This is important because I game on the PC so I need the 100Hz to work on that side.
I don't need that on the Mac since I only use the mac for editing video and audio.

The other thing is, everytime I want to switch machines I have to switch the inputs on both monitors. This sucks. There has to be a better way to like press ONE button and switch over without having to reach for the buttons on the monitors.

I already have to swap keyboard and mouse which is enough of a pain...

The whole reason I have to do all this, is because I don't have space here to have two desks.

 

HELP.

 

[GM Rod]

Nobody?