Most stores that sell these bonsai junipers are misinformed about caring for a juniper, and therefore pass along this misinformed information to it's consumers. Junipers and all other conifers belong outdoors. They are not indoor trees.
Carefully remove the tree from it's pot, and give the roots an inspection. If they are just as dry, and brittle as the rest of the tree then it's a lost cause. Don't forget to search the forum for other tips, and advice on how to care for them. They're fairly easy trees to care for, but as an outdoor tree only.