I have a 900p monitor, but whenever I start a game it puts the resolution to 1080p which results in the monitor not being able to provide display. I have to manually edit the config to 900p to be able to play games.
Is your monitors native resolution set to 900p? It should automatically configure the resolution to your systems set resolution, except if you're playing much older games. A lot of newer games set the resolution to 1080p as it is still a popular resolution to play at. I mean, I don't know why manually setting the resolution is a problem, it doesn't take that long. Hope this helps.