Oh joy and happiness! For some reason VLC started taking ages to load on my 2 PCs. I uninstalled it and now just use the Films & TV app which works fine for playing back all video files of interest...

I'm not aware of any PC monitors which can be dimmed like a laptop display. Can you try connecting your monitor to another PC to see if the monitor will enter standby on a different PC? This will...

What monitor and GPU are you using?

I would first try reinstalling the drivers for your GPU and monitor (if it has any).