Without even fishing your message I immediately think that your culprit is overwatering. Watering everyday is most likely to much water. A tree with needles is naturally a tree that is suited to an environment that is prone to drought.
Anyway, test the soil with a toothpick by immersing the toothpick into the soil. If there is dirt sticking to the toothpick when you remove it, don't water.
Here are two prefered watering techniques:
1) Overhead watering: Use a watering can and drench the surface area of the soil with water until water exudes from the lower pot holes.
2) Immersion: Fill a sink with enough water to emmerse the entire pot. Place the tree (pot) in the water and let sit for about an hour.
Might as well put a third method in here as well:
3) Misting: You can buy a little mister and mist your tree as well as the above two methods.
Also, window sills are bad for bonsai. The temperature extremes that they have to endure between day and night cause the trees to be very unhappy. If you tree is actually on the sill, I would suggest moving it away from the window. Maybe get it a little table.