Unfortunately by the time that a Juniper gets to this point it is already dead and probably has been for some time. Consider a Christmas tree and how long it can look reasonably healthy after it has been cut down. You don't say specifically how you have been managing it but I do know that the instructions that come with mass produced bonsai are notorious for being inaccurate. Two of the most common issues are placement and watering.
Junipers kept inside will almost invariably fail. Watering should not be done on a schedule, especially if the tree is potted in the usual peat based potting soil. During the summer I water most things everyday but I have my plants in a very open, free draining mix. Even so, there are days when it may be overcast or it rains, that I don't water that day. You have to check and then make the decision whether or not to water.