When your onscreen keyboard is not poping up on your tablet when you are trying to type, tablet thinks there is a physical keyboard plugged in, so it wont bring up the onscreen keyboard. Here is steps to enable the onscreen keyboard.
Go into Settings on Tablet
Scroll down until you see Language & input
On the right hand side you will see option called Keyboard & Input Methods
Pop up will appear "Choose input Method"
There is an option called Hardware (Physical Keyboard) ON/OFF
Turn "OFF" physical keyboard
Now you should get your on screen keyboard on your tablet