Beginner Gardening: Madagascar Dragon Tree- leaves turning brown/ yellow, 1 by kookum

kookum wrote:
I recently purchased a Dragon Tree, which was perfectly healthy when I brought it home. Within 2 weeks, the leaves have turned yellow and now brown and dry at the tips- what am I doing wrong? It is always beside a big window, I fertilized it once, and water it every 1-2 weeks. The temperature in the apartment is usually around 15Celcius or warmer, and quite humid. Is this too cold for this plant? Thanks in advance for any advice.