This describes a working solution for Inspiron 15 3521. Perhaps will work for you. I am having the same problem and am about to try this.
Hello. I was facing the same issue that you were facing. The comments mentioned above me did not solve my problem.
Instead, i came across this site, download the bluetooth driver from here for Windows 8.1. It is the one that is around 250mb. Install it, it provides the necessary drivers and enables the laptop bluetooth! I hope this solves your issue as well