If it happens that the first thing to do is calm down, no good to be nervous, we will try to fix it (if you got a comment to let us know if you was useful).
It may be that after restarting your iPhone, iPad or iPod touch you find that does not load the home screen or just the screen goes black. We can do two things:
Forcing a reboot. To do this we press the power button and the home button simultaneously for more than 10 seconds. This would force the system to reinicarse. Perhaps with this and you've arranged, but have to put it into Recovery Mode.
button start and a power cycle
Put the device into Recovery mode. This is the last thing to do, eye, only do so if all else has failed and you are very calm to do so. To start the Recovery (Recovery) so we have to push the button on / off while the Start button, and while the screen goes dark and then let go only on / off (top) and we hold the Home button until you get a USB connector on the screen as the image. From here we connect the phone to a computer with iTunes and proceed to recall. EYE, you will lose all data, you can retrieve the last copy you have, but do not know if that's what has caused you to have these problems, so you may have to do several tests before they are 100% operational.
Yossi recovery mode at all else fails, drop a comment and see if we can help with any particular point.