I have the same problem and solved it with this driver. It work for win 10 on my DELL XPS 1645 - Dell Wireless 370 Bluetooth Mini-card. [URL]  
I updated to windows 8.1 and Bluetooth was mysteriously gone. When i try and install my old win7 drivers, it comes up with compatibility issues, even if I set compatibility to vista, xp OR 7.
Bluetooth not working in Windows 8.1 for Studio XPS 1645