Why is my screen black, and why can't i click anything?

I was messing around with my settings on my computer and I hit the full screen button in the settings. My minecraft disappeared and all I saw was my Desktop. It won't let me on and it happens every time. I've tried to install minecraft twice now. I don't have any mods I haven't done any thing.

Not sure if you got a virus or not. Try unplugging for 10 mins and try again.

Make sure cable is properly connected from your c.p.u. To monitor.

Turn computer off, Remove Battery and Hold down Power Button for 30 seconds. Then put all back and start computer.