Plant's stem becomes hollow, then it falls over. Mostly affects corn stalk plant.
Your corn plant, aka Dracaena massangeana, looks to be suffering from root rot. It is moving up the plant from roots, into stem; eventually it will get to the leaves. The cause is soil that stays too wet. Once the stem starts to get soft, there's not much you can do to save the plant. If you can find stem that is not soft, you can cut the plant there, remove the leaves at the bottom, and stick the cut parts into some new, fresh potting soil, and there's a good chance the cut parts will root. Keep the soil slightly damp until you see new growth starting, and after that, allow the soil to dry more between waterings. In the future, test the soil for moisture content by using a moisture meter, or a wooden dowel; insert all the way to the bottom of the pot; the soil should be almost dry before you water again.