Sometimes we hear of stubborn tomato and pepper plants that get plenty of flowers, but that just won't set fruit. The first thing to check for is proper pollination, but if you're sure you're pollinating, here are a few other things to try:
1) The most usual suspect with lack of fruit set is not enough light for that plant in that environment (water, temperature, etc.). Make sure your bulbs are new and that the lights are as close as possible to the top of the plants. More light equals more fruit.
2) A rinse and refill (when the nutrient light goes off, empty all water out of the reservoir and refill with fresh, cool water and a new nutrients). This re-balances the nutrients.
3) Move the garden somewhere else. A different window, a new room, different temperatures all can impact whether a flower turns into a fruit.
4) If you are using distilled water, add some tap water. If you are using tap water, try some distilled water.
Sometimes, with a fruiting plant, it's hard to determine exactly what is causing the fruit not to set. By changing a few environmental factors like light, water, etc., we often have success in getting a stubborn plant to fruit.
Try growing your tomatoes with these seed pod kits: