Tried everything

Ipone 4 turned off while on a phone call and wont turn back on. Tried holding each button and both buttons simultaniously for over a minute each time. Plugged into computer and not plugged in. Guess ill have to go to the Apple store and try to get a new one but will they be able to recover all of my contacts, pictures, files from my old phone when they have it. I have some things on my phone meant to stay private and dont want them to get them when I trade my phone in.

 

it was plugged in overnight and only unplugged for 15 minutes. Fully charged