Is it PLUGGED IN to a working outlet, and have you pressed the power button again?
If your computer is RUNNING SLOW, Have you tried restarting? If a computer has been on for too long, it might have used up some resources that need to be cleared.
If you CAN’T LOG IN, is caps lock enabled?
Is your computer UP-TO-DATE? If it asks to update, there is usually a good reason. If you saw the update and told it to go away, press the Windows key on windows and search for Update, or press the ⌘ key and space and then type Update. Then, there should be a button to update now.
Have you restarted recently? This clears up all the things the computer is thinking about. Be careful to fully restart it, and not just put it to sleep.