Sounds like your phones system has been damaged or erased. That wouldn't happen through normal usage. Did you root the device or perhaps try to install a version of Android that wasn't an update through the phone? These can cause this problem.
As long as the phone isn't damaged (and the storage isn't) the only way I know to fix it would be to either unroot the device (if it will let you) and then "Hard Reset" it or reinstall the OS on the device through another means. Say the SD card or connected via USB to a computer.
For further details on that, I would suggest posting your problem in the "Rooting, Jailbreaking & Unlocking" Forum.
http/www.tomsguide.com/forum/forum-117.html Yes I know it is under phone, but they use the same OS so it should still apply.