I am trying to grow ginger and in the last three weeks the leaves turned brown. What is happening to my ginger? The rhizomes appears to be fine and no rot. In addition, I water them once every two days (Average temperature is around 25 Celcius)
Usual cause is either a light problem or insufficient organic matter in the soil. Regarding sunlight, they don't like it - what they want is diffuse or dappled bright light for a minimum of 5 hours a day, so if yours have been getting a lot of sun, that would explain the way they look. On the other hand, a totally shady spot isn't any good either - they do need bright light, just not bright direct sunlight.
Otherwise, they like a high level of nutrients, so in the ground, soil enriched with composted manures and the like - in a pot, fertilisers on a regular basis, particularly those higher in potassium, since its the root you're trying to cultivate. My money's on the light being the problem though... but you'll know the conditions better than I!
In addition (kinda hard to see with that picture) old stalks die, new ones grow (one of mine is over 21 years now, though it was 16 before it flowered as it was not getting enough light (based on it flowering immediately after getting moved to a brighter location, and what the offspring do.) So some death/browning is perfectly normal.
Depending on size of pot and size of plant, you might be watering a bit too much (small plant, large pot, lots of water storage and not much water use) but again, I'm guessing as best I can from your picture.
Ginger needs a a big pot; it really wants to spread out. When I grew ginger that I brought from Asia in Belgium, I used really big pots in the living room in a half sunny spot in winter and planted it out in May, to dig it up in September. Only during these months it really made a lot of progress, the potted version grew mainly leaves.
I will take the other hint on board; mine makes no root growth to speak of here in Costa Rica at 780m altitude.