So a couple of things might be causing this issue. For starters, you're going to want to Power Wash your device. If something like an application is causing your CPU to be bogged down that might be the culprit.
I would also open the device up and check to make sure the keyboard cable is seated correctly. In addition, I have seen a few Chromebooks where the ribbon cable for the keyboard is creased by the battery. This causes damage to the cable and will result in the connection to the logic board not being complete. If you do open the device up definitely take pictures and upload them here.