I did an in-place upgrade of El Capitan to Sierra a week or so ago. Everything seems ok except for Bluetooth. It's completely non-existent. I've tried re-installing Sierra, SMC reset, and NVRAM reset. I've tried deleting the bluetooth plist file. When I go to About this Mac and select System Report, the Bluetooth section under "Hardware" says "No information found". When I go to Bluetooth in System Preferences -> Network, Bluetooth is off. The option to "Turn Bluetooth On" is greyed out. Bluetooth was working fine before the upgrade and now it seems there's no driver or anything installed. Any ideas?