My computer isn't working, what do I do?

My laptop has recently stopped working. What happens is I'll turn it on, it'll go the the start-up menu, I'll select the way to start the computer up (I've tried every way to start it), and it'll go to a small loading bar with "Windows" under it, and the bar will not go away and nothing will happen. The bar wil keep moving with the little green sashes but the screen will stay the same. I kept that screen on to see if it would change, and 8 hours later it stayed the same. I haven't tried anything yet so what can I do to fix it? The only info i have about it is that it's an HP brand laptop.