There are many reasons why keys might get stuck on a digital piano, but the most common reason is that dirt or debris has gotten caught in the key mechanism and prevented it from moving. This can occur if the piano is sitting unused for a period of time, or if someone has tried to clean it without first removing the keys. Occasionally, keys can become stuck because of waterdamage or corrosion, either from rain or moisture seeping into the keyboard's workings. If you experience any of these issues and your keys don't seem to be responding well to standard cleaning techniques, it may be worth taking your piano to a professional technician for a deeper inspection.