My monitor won't display anything

The problem started when I turned on my computer, and noticed that my screen resolution was different for some strange reason. I changed it, and then loaded MS. When I loaded MS, instead of seeing the game, the screen turned black and I got a grey floating box telling me that the screen resolution wasn't right or something. So I decided to restart my computer, and suddenly my monitor won't display anything. Everything's working just fine, it's just that nothing shows up on my monitor.
Does anyone know how to solve this problem?