Nothing is going to send a chill down the spine of an iPhone or iPad owner more than going to use their device and finding that it isn't working. Fortunately, most "bricked" devices can be brought back to life with a little know-how.
Here are the steps I take when trying to bring a dead iPhone or iPad back to life.
First off, remove the device from any case it is in. Why? Because I've seen cases cause problems by holding down buttons or causing devices to overheat. Also, it can be hard to press the buttons to do a reboot while the device is in the case.
Next, put the device on charge, because the problem could just be a dead battery.
If the device is still unresponsive, the next move it to attempt a reboot it. Do this hold the power and home buttons simultaneously until the Apple logo appears. If the logo doesn't appear after 30 seconds or so, well, this hasn't worked.
If your device is still a brick, the next thing to try is DFU (Device Firmware Upgrade) mode. To access this mode, first make sure that the device is switched off. With the device is off, press and hold the home button whilst connecting it to your computer with iTunes already running. When you see the USB cable with an arrow towards an iTunes logo appear on the screen, you can let go of the home button. If this works, attempt a recovery of the device through iTunes.
An alternative way to enter DFU mode is to connect the device to the computer running iTunes. Then, with the device off, hold the power and home buttons for 10 seconds then release the power button while continuing holding the home button for 10 more seconds, after which let go of the home button (note, these timings are important, so be looking at a clock when while you're doing it).
Still no luck? Don't give up! Try the DFU mode recovery again just in case.
Your device still bricked? It might now be time to take it for some TLC at an Apple store or authorized Apple repair center.
Note that doing a recover via DFU will wipe the device. If you need a good reason to make a backup of your iPhone or iPad, think about how you'd feel if you lost everything on it.