My ipad isnt turning on

Hello,

my ipad 4th generation battery is completely low and shut off while i was sleeping. so i put it on the charger is been charging for more than 24 hours but all i get is the low battery sign then the apple logo comes up then it shuts off and it keeps repeating that. tried plugging it up to my computer and doing an update though itunes but it shuts off before i can complete it. please help my wedding stuff is on there and i need it thank u so much