You are experiencing what is called a SWOD (Spinning Wheel Of Death). All is not lost! What you’ll need to do is get it in DFU (Device Firmware Upgrade) mode and restore.
This is the easiest way to boot into DFU mode :
* Plug iPhone into PC (or Mac)
* Press-and-hold the sleep button and home button until the device force-powers off. (about 10 seconds)
* Release the sleep button, but still hold the home button. Do this until you hear the device connected sound on the computer.
* You may now release the home button, to test that it works, go into iTunes, it should say that an iPhone is connected, and has to be restored.