ANY IDEAS?!?! My Iphone 5 won't start and is stuck on the apple logo.

My Iphone 5 has a broken lock button so I use assisted touch. I charged my phone fully the night before, used it as an alarm to wake me for work and then when I went to check the time, the screen was black. I tried plugging it in thinking maybe somehow the power got drained, but nothing happened. A few hours later I tried touching the home button and the apple logo popped up and hasn't changed. I unplugged it and it's still there. I tried connecting it to itunes but it says that the device has timed out so I can't get into my phone that way. I have no idea what's wrong any ideas?!