Macbook Pro 2017 won't connect to ASUS ProArt monitor (I think it's pa238) via HDMI?

I have had my monitor for a few years now using it with my Windows PC. I recently bought a Macbook Pro 2017 model and wanted to hook it up. I bought the HDMI adapter and plugged it in and my Mac screen flashes black then back to normal, but the monitor stays black and isn't usable. I can see in the displays that it is connected but it doesn't work. Any advice would be great - thanks.