After a lot of use, the ribbon connector for the keyboard may be damaged along the 2 folds. If re-inserting the ribbon cable only has temporary effect or only works for some keys, see what happens if you raised the keyboard so that the folds are straight. I needed to find a way of keeping the folds unfolded just enough while simultaneously being folded in the case. Yes, this is a design issue with the chromebook whereby the flexing of the keyboard during normal use causes the folds to become increasingly problematic. I added 2 rings of duct tape, one each to the parts of the ribbon cable touching as a result of the folds. I assumed this would hold the folds straight enough so that they would work: Works fine now.