Why isn't my iPhone fully turning on?

Okay first of all, I am a Music producer and love to keep memories. So I've had my iPhone for quite some time and I've taken so many photos that mean so much to me while I've had it, and it kills me knowing that I'll never see them again. I also have an app I use for music that has all of my beats on there that is worth much more than anything to me, possibly get me to where I want to be in my career for music. Only problem is that my iPhone has been dropped twice and the first time I was able to fix it by simply plugging it in a wall charger and restarting it. But the second time, the iPhone would turn on at 100% battery but would turn off eventually or when I unplug it. I've tried over and over again to see if it would work, but it didn't. Now when I plug it in and I turn it on, it stays on the apple logo for 15-20 seconds and turns off and repeats. I'm really scared right now, I don't care about the phone, I can't lose those photos or my music, please help!