Bluetooth unavailable with Yosemite 10.10.3 Bluetooth is unavailable since the middle of last March.

I've followed all topic suggested: reset SMC, PRAM, deleted preference files (com.apple.Bluetooth.plist), reinstalled OS X from scratch and I also changed the WiFi-Bluetooth board with a brand new one. Nothing worked.

At first resetting SMC worked, but than the trouble came back; same thing happened when deleting preference files. After the WiFi-Bluetooth board replacement, when I turned the MacBook on, bluetooth was unavailable so I turned WiFi off and bluetooth showed up, but after some tens seconds it was unavailable again and never came back.

I've run the AHT, both the fast and the more detailed one, they reported nothing wrong.

Is there anyone who can help me with this?

My configuration:
MacBook Pro 15" Mid 2010
OS X Yosemite 10.10.3
Try these commands on a terminal window to unload and reload the driver:

sudo kextunload -b com.apple.iokit.BroadcomBluetoothHostControllerUSBTransport

sudo kextload -b com.apple.iokit.BroadcomBluetoothHostControllerUSBTransport