There are other questions about this and not much in the way of answers. I have an early 2015 MBPro which has always worked fine with BT mouse and keyboard, but it suddenly not connecting at all to anything. Have tried the usual litany of remedies (deleting files in both PREFERENCES folder, the RESET thingie, a couple more alternatives, and no joy. Have recently erased SSD and reinstalled Mojave (twice) and restored from CCC and on 2nd occasion via a backup drive. No joy. I can't turn BT off (that button grayed out) and I'm about at end of rope. Can't buy a clue. All advice appreciated.