we had a keyboard related pop-up which my young daughter closed before I could read it. Now the keyboard doesn't work properly. If you hold a button down for a while then the letter appears, what could be wrong?
I would recommend trying to clean it out and see if it improves. Easiest way is turn upside down and shack out the "dirt" than below out with compressed air. Keyboards can get dirty causing the keys to become unresponsive after time.