HEY EVERYONE I just had the same issue of an old iPhone 5 that I was on reserve for emergencies so I have not used it in a year, What i found to be the charm was warm it up (i just used my laptop that was quite warm underneath as all laptops get, left it there for 1-2 mins resting underneath then i held down ALLLL THE BUTTONS ON MY PHONE(home button, + - buttons and main top switch) and after what felt like eternity it came alive!!!! :) Really hope this current advice helps others!!