Can I fix my sad-looking dapple willow?
Willows are usually pretty tough. When you say three years old, I am guessing that it is how long you have owned it, not its age. Examine the dead limbs and look for disrupted, swollen wood or holes and sawdust-like frass. There are several kinds of borers that will get into older wood on the shrub.
Prune out the bad stuff as low to the ground as you can without going into the ground. Leave an angled cut at the bottom so water can run off. If the willow is in any kind of decent shape, it will send up some new shoots. This may have already happened. If it continues to decline, it was probably beyond fixing. Life in the horticulture world is sometimes tough.