I FOUND A SOLUTION!!
(the paragraph bellow just explains my situation)
I have an iPhone 5 with a lock button that doesn't work. One day I woke up after a night of it charging and it turned on just fine. The next second, it turned off and wouldn't come back on with the home button. So I plugged it in and nothing happened. Of course I couldn't reset it because my lock button doesn't work. So I decided to try something...
I left my phone unplugged all day. And then all of a sudden the symbol to plug it in to charge appeared so I plugged it in and now its fine.
p.s. the symbol came up right after I touched the screws on the bottom with a metal screw driver (not sure if that had any affect)