Help Unfortunately system UI has stopped

[Hender]

I am unable to get passed my lock key screen. Once I have put my 4 pin code in, the screen goes black for 2 seconds and when it comes back on the lock key screen is there again. Please help.

 

[girolez]

Hi

Have you tried rebooting the device (power off - wait 20 secs - power back on)?

 

[ThePhizzle]

What was the last thing you did on your device before it started this problem, you didn't try placing another UI on the device? Is the lock screen the only visual you get? When do you get the UI error message? Before or after you typed in your pin?