That is why we always ask customers to send units back so we can test it, regardless whether the unit is still under warranty or if the unit is modified. We DO NOT charge a fee to find out the problem. I don't understand why some people don't take advantage of it. In your situation, I also think it is either the touchscreen controller or the flat ribbon cable. It's hard to know without seeing the unit as your unit is a few years old. The touch overlay rarely fails. If it is the flat ribbon cable that failed, we can also make some modifications to the unit that our new units have which greatly improve the durability of the flat ribbon cable. We can also see if you can trade in your unit for a new one. We are always trying our best to help our customer. Please don't hesitate to contact us.