If your iPhone, iPod Touch, or iPad is stuck on the Apple logo boot screen, follow these steps below to restore your iDevice to its former glory.
Step 1) Plug in your iDevice into your computer using the USB cable.
Step 2) Press and hold the sleep/wake button and the home button simultaneously. Continue holding until the screen turns black and keep holding until the Apple logo reappears.
Step 3) If this does not work and the iDevice is still frozen on the Apple boot screen, follow the instructions here on how to put your iDevice into DFU mode and then from there, restore your iDevice using the guide here.