Is it built-in or USB? Either way I'd probably look in the device manager to see if it can see the BT adapter, and if so reinstall its driver, preferably from the manufacturer's website - if you can find one. If it's up to date try an older one. It doesn't always work though; since I had to reinstall Win10 on my wife's laptop I can't get the trackpoint to work even with Lenovo's own drivers.

If it can't see the BT device at all it could be that it's been 'killed'. It's usually only laptops that have killswitches - often a function key that switches off all 'radios' - wifi and bluetooth, or either of them. (This is another thing that doesn't work on the Lenovo.) So when you've exhausted drivers investigate that. (Google 'rfkill windows' or similar.)