I activated VoiceOver and locked my iPad mini.
But it won`t be unlocked again.
There`s a Black square there, but I can´t do nothing to unlock it.
With VoiceOver on you need to use a tap-to-select and then double-tap to activate/type process e.g. for your passcode tap the digit that you want to type and it will get the box around it and then doulbe-tap the digit to type it. You can then use that tap-to-select and double-tap to activate process and 3 fingered scrolling to go into Settings > General > Accessibility and turn VoiceOver 'off'.
Or you should be able to turn it off by connecting to your computer's iTunes : http://support.apple.com/kb/HT4064