Here’s how to put an iPhone into recovery mode and get it out of recovery mode in iOS 8. (It also works for phones running iOS 7, and you can also do this with an iPad. The video above shows the process in iOS 7, which is the same as iOS 8.)
1. First, make sure iTunes is up to date on your laptop, PC or Mac. Then, connect a USB cable to your computer, but don’t plug it into your iPad or iPhone just yet.
2. Turn off your iPhone or iPad by holding the sleep/wake button until the red bar appears: swipe to the right to shut down your device.
3. Connect the USB cable and continue to hold the home button.
4. You will see the Apple logo appear, and this will change to the recovery graphic:
5. You can now release the home button. Your iPhone or iPad is now in recovery mode, and iTunes should be displaying a message to say as much.
You can now use iTunes to restore a previously saved backup to your device.
How to get out of recovery mode in iOS 8
To get out of recovery mode, make sure your USB cable is connected to both the laptop running iTunes and your device.You may need to hold the home button while connecting your USB cable as above.
Now hold the home and sleep/wake buttons together until you see the Apple logo appear. Don’t let go until then – it can take several seconds: the recovery graphic will disappear and a black screen might be shown for a while, but keep holding the buttons down until the white Apple appears.
Leave the USB cable connected until your device boots up and shows the lock screen. It’s now out of recovery mode.
If this doesn't work - it may or may not depending on your iPad or iPhone's problem, there are other utilities such as TinyUmbrella which claim to be able to exit recovery mode without losing all the data on your iDevice.