Sorry to hear about your trouble with your Weeping Cherry tree. It sounds like it may
have gone into some type of shock. This is
not uncommon after a few months for new
trees. A couple of questions, how were you watering the tree when you first planted it? What type of fertilizer did you use? How often
are you watering it?
A solution for you is you might want to take a leaf or two, and a small branch and bring it to your local nursery or garden center. They may be able to identify the problem.
You can also take a small knife or your fingernail and scratch the surface of a branch or the trunk. If it is green, it is still alive. If it is brown, it is in stress.
Do you have any other plant specimens planted near by in your landscape or garden? Sometimes I will recommend to my clients to have their soil tested to see what nutrients the soil may be lacking.
I recommend also when planting a tree to water the first couple of weeks with a slow drip hose. Water about 20 to 30 minutes and rotate the hose around the base every 5 minutes or so. This will allow the entire root system to get moisture. Adding organic mushroom compost to the soil will also help. Mushroom compost is an organic fertilizer that will last up to one year.
Let me know how you make out, and please feel free to continue communicating here at landscape solutions website. If anyone else has some other suggestions for Ryan, please feel free to commit. Hope your tree survives!