Have you tried the keyboard on another device to see if the keyboard is still working correctly? If it isn't, then the keyboard is the problem. If it works with another device, then there would be something else causing it.
If the keyboard isn't the problem, you could "possibly" clear cache in recovery to see if that helps? To do that do the following...
1. Make sure the device is turned off.
2. Next, press and hold down the "Power" button until the device powers on, then (while still pressing Power) immediately press and hold "Volume Down".
You will see the word Start with an arrow drawn around it.
3. Then press "Volume Down" twice to to choose "Recovery Mode".
4. Now press "Power" so you can resart the device in "Recovery mode". You should see an image of an Android robot with a red exclamation point.
5. Next hold the "Power" button down and press the "Volume Up".
You should now see the recovery menu.
6. Use the Volume buttons to move up and down and highlight/choose "Wipe Cache Partition", then press the "Power" button to execute.
7. When that is done, highlight/choose "Reboot System Now" and press the "Power" button.