My iPhone won't come on? Help?

Okay, my iPhone was going really slow and not working right. So I turned it off and turned it back on. When I first turned it on it wouldn't come on, it was a black screen but it was still lit up. That wasn't a problem. I knew how to fix that. Then, I tried turning it back on, and it won't come on. It been stuck on the screen with an apple for about 5 minutes. It went off, and came right back on with the apple screen. What do I do???