I had the same problem. Unable to shut down (or taking ma-aaaaaany minutes) my Dell E6410 with Windows 10 installed. Took me 2 days searching, but than found the solution. The Wireless WWAN Card (sort of GSM network card, I don’t use it, but is installed in my E6410) is causing the unable to shutdown problem. I removed this hardware (could not find how to disable it in the BIOS), and than the problem was away. Removing this hardware is shown in this video: https://www.youtube.com/watch?v=hU66rWRFjSg&feature=youtu.be
Hope’s it works for u to!