My IPhone 6s has been sitting in my drawer for almost 15 months (not used). I connected it to wall charger yesterday and the Apple logo appeared, then it turned off. It's stuck in this loop indefinitely. When I take out the charger, the screen goes black instantly. If I try to connect it to a Mac for recovery mode, it won't even turn on (maybe USB power supply isn't enough to fire it up). Holding "home+power" buttons method (when connected to wall charger, not mac), it shows itunes and usb logo. Any suggestions how can I fire it up through mac? I've googled and looked up how to use recovery mode or "DFU" mode but it may only be possible if I can make it turn on through the USB port on mac. Please help! Thanks!