every thing plugged in all the way?
1) Wall to Computer
2) From computer to: keyboard, mouse, monitor and whatever else.
things don't work try turning them off, waiting a couple of minutes
or even more. Then coming back and seeing if they work.
If you use a roller mouse and it gets dirty use only a round wooden
toothpick and compressed air to clean it.
something works don't fix it.
If something doesn't work relax, juggle and don't forget to breathe
while you wait for help.
if you must fix it here is some very general advice about fixing hardware