fork questions

ExTrEmE BiKeR

the forks i have on my bike right now are dart 3s. the manufacturers website says that they have a 100mm travel yet the most possible travel i can get out of them is what i measured to be about 40mm. how come they dont compress all the way? ive been playing around with the preload and rebound adjustment a bit lately. does either of those things have anything to do with travel? what can i do to get the full 100mm or close to that out of my forks? do i need to get a longer travel fork? i was thinking of something like the recons which have up to 130mm of travel if i cant get these ones to travel more