I got a gateway computer stuck in a loop!?

Hello,
just stat off this problem was my fault and I've tried everything i can think of to fix it without help and nothings worked i started it up after sitting for awhile and i let it update a service package and it wanted to restart i let it well it was taking forever and it says do not turn off well... u can guess what i did there and now every time i turn it on it goes back to that same thing then shuts down and restarts and does it all over again and jus keeps doing it and I'm stressing out please help!