Why is my cornstalk plant turning brown?
I can only guess what kind of plant you're really talking about. From what I can tell, it's a dracaena, which is also called a corn plant.
This article covers detailed information on growing all types of houseplants. http://content.ces.ncsu.edu/indoor-plant-selection-and-care.pdf
It indicates that dracaena needs moderate light.
Arkansas Extension says the following: "Dracaenas are popular, easy care houseplants. However, they are very sensitive to fluoride toxicity. Most of the time the fluoride source is from fluoridated tap water. However, superphosphate, perlite, and some peats are also sources of fluoride. Fluoride accumulates in the tips of plants and prevents the stomates from closing properly. Necrotic lesions, tip burn and marginal chlorosis, followed by browning of the leaves are common symptoms. Fluoride toxicity is seldom fatal. Sensitive plants should be watered from a nonfluoridated water supply.
From the University of Washington, here's a response to someone's question about her dracaena turning brown, and it's a good answer: "We cannot diagnose plant problems via email. However, we may be able to give you some ideas of what might be happening. The browning leaves could be the result of too much or too little water. The soil should be kept lightly moist, but avoid overwatering. Avoid giving fluoridated water, as this link from University of Vermont suggests this plant is sensitive to fluoride. It is also sensitive to temperature changes (up or down) and should not be near heating or air-conditioning vents. Repotting may have caused some stress to the roots."
I hope this helps. Remember to NOT let the soil dry out completely, but don't keep it soaking wet all the time, either. Good luck!