I hate to be the bearer of bad news,but marginatas (I'm making the assumption that when you say dragon tree you mean dracaena marginata)are famous for getting a really bad smell when they have contracted stem rot, and they get rot really easily if they're overwatered, and once they've got rot they're pretty much goners. Does the stem have a sort of wrinkly appearance, and kind of soft? Are the leaves dropping off a few at a time? With marginatas, you have to test the soil for moisture all the way to the bottom of the pot, not just on the surface of the soil. Use a narrow wooden dowel, or a bamboo kebob skewer if its long enough to reach, and use it like testing a cake. When you pull it up, there should be only the faintest trace of moisture when you feel it. You can try cutting back the moisture to let the plants dry out - sometimes they pull through. If not, don't be afraid to try again.