Lower screen inaccesible

Here's a strange one! I have an elephone P6000 running lollipop five. Yesterday, I got a text which, when I tried to reply to it, found that the reply text box wasn't accessible? I could see the box,, but no matter how I tried, I couldn't activate it to pop up and present the reply keyboard. It's not a screen issue, as that part of the screen is usable on many other apps. I have since found I can't use WhatsApp for the same reason. Also, if I go to settings, the very last item is 'about phone', this also doesn't respond to taps ( yet if you slide the menu down one item, you CAN access the next item by tapping the bottom of the screen????)
Any ideas please?