This has happened to me a few times during the summer months when i have my window open, so far it has always been little midges/corn flies, all i do is unplug my monitor and lay it face down on the floor over night and make sure the is no light visible to the front of the screen, leave your room light on, the stronger the better, i use my bathroom as the lights are really bright in there and hopefully it will climb out of the vents on the back and head to the light, best of luck m8.