IOS 8 blocked my phone
Phones can and do crash and need help from iTunes to be restored even if no software change has happened. The most common cause of a failure to update was that the phone was already missing a system file and the update just was the "messenger" that checked that file for the first time in a long time.

Why not connect it to a computer with iTunes and then restore the OS to clear out any errors? That will rapidly determine if your problem is a temporary software issue or a deeper hardware problem:


http://support.apple.com/kb/HT1414 - Use iTunes to restore your iOS device to factory settings