iPad won't register touch only for the unlock passcode screen

I Know it can't be the screen touch, mainly because I can slide to unlock perfectly; however, when I try to press in my number passcode it won't register that I have touched it all because it doesn't show up. I have tried rebooting it etc.

It happened after it ran out of charge so it was fine before, it is now charging but that is when it started causing the problem.