Q: Bluetooth won't turn on

Try resetting the SMC:

Reset the System Management Controller (SMC) on your Mac - Apple Support

- Try starting in Safe Mode

OS X: What is Safe Boot, Safe Mode?

https://support.apple.com/en-us/HT201262

- Boot to Recovery and repair the startup disk

OS X: About OS X Recovery - Apple Support

https://support.apple.com/en-us/HT201314

- If it is repairable reinstall the OSX

How to reinstall OS X on your Mac - Apple Support

https://support.apple.com/en-us/HT204904

- If you do not have a backup use disk utility to restore the internal disk to an external disk so you can try to recover data.

Then format the startup disk and do a fresh install of OSX

If still problem, make an appointment at the Genius Bar of an Apple store since it appears you have a hardware problem.

Apple Retail Store - Genius Bar

https://www.apple.com/retail/geniusbar/  

This is the Mac Pro desktop forum. I requested your post be moved to the MacBook Pro laptop forum.

Open system preferences > bluetooth & click on advanced have you checked the settings in bluetooth .

a screen shot is there for reference :

An apple article is there : Set up your Apple wireless devices - Apple Support