What species is it? It sounds like the plant is dying from bottom-to-top with no new growth which leads me to think it's dying too little light and/or root rot, though it's hard to say based on the information and no picture. Here's a few questions:
1. LIGHT:
a. What type of grow light (fluorescent, incandescent, etc.) and how many watts?
b. Is this the only source of light the plant has?
c. How far from the plant is the light and for how long is it turned on?
2. WATER:
a. What do you water your plant with (tap, distilled, etc.)?
b. When do you water? Is the plant constantly sitting in water, soil always moist, or do you wait until its dry before watering again?
3. FERTILIZER: Have you ever fertilized the plant and, if so, how many times and with what?
4. BUGS: Do you notice if there are any bugs or webs on the plant, or does the top of the soil look nasty and slimy?
5. HUMIDITY, TEMPERATURE: If you bought the plant from this forum, it's probably a tough variety, so these parameters probably aren't the cause of its decline, unless really extreme.
Answering these questions will help us determine what's causing your plant to decline.