Well, a few possibilities. The bulb could have rotted and the leaves died. But, If it doesn't smell bad, it could have just gone into its "winter" dormancy a bit early, triggered by decreasing day length. My suggestion would be to stop watering it, put the potted bulb in your basement or another place where its cool (but not below freezing) and dark. Bring it out again in Oct or Nov, repot it into fresh soil, water it in , put it in a sunny window, and see if the bulb puts up flowers and leaves. Normally, in the North, you force dormancy in late summer or fall, to get Xmas blooms. Your bulb may have done it on its own. If your bulb was purchased in the fall of 2014, it may not bloom again this coming Xmas. It can take 2 or more years before the bulb has enough reserves to make new flower buds (made deep in the bulb in the summer). New bulbs have been specially forced for Xmas blooming. It can take a while for the bulbs to recover from that extreme forcing.