Make sure to have a backup of your device first, you WILL loss all you data, contacts, pictures, applications, music, everything...
What is DFU mode?
DFU mode is a state that you can put your iPhone/iPod/iPad into where it can interface with iTunes but does not load the operating system or boot loader (this is what really differs DFU mode). DFU stands for Device Firmware Update.
What is DFU mode used for?
The primary reason people need to access DFU mode is to change the firmware on the device. It is also used to clear up any software errors and reset everything.
How to enter iPhone DFU mode
- Connect the device to your computer and launch iTunes
- Turn the unit off (hold down the power button at the top of the device)
- Hold down the sleep/power button and home button together for exactly 10 seconds, then release the power button
- Continue to hold down the Home button until a message appears in iTunes telling you an iPhone in recover mode has been detected
- When you are in DFU mode your screen will be completely black
Even though the screen is black, that doesn’t mean the device can’t be interfaced with either iTunes or a custom firmware client (for jailbreaking, etc).
Remember that if you see the restore logo, iTunes logo, or any message on the screen, you are not in DFU mode but standard Recovery Mode. Again, DFU mode is signified by having a completely black screen on the device. If anything else is the case, repeat the steps above until you enter into DFU mode successfully.
Exit DFU mode on iPhone/iPod/iPad
The simplest way to exit out of DFU mode is to hold down the Home and sleep/power buttons on the device while connected to iTunes. Then just hit the power button as and this should reboot the device as usual.