So the driver software you can install from TP link technically works (https://www.tp-link.com/ca/support/download/ub400/#Driver), but let be honest it is very slow. Audio output to my bluetooth headphones is constatanly out of sync by 1-2 seconds at worst. The real problem with the TP-Link's driver software is that it can only pair with one device at a time, and the pairing process is forced to have to connect only using the bluetooth icon in the taskbar.

The latest Windows 10 update #2004 broke my bluetooth setup completely, and the TP Link 400 stoppedworking.

@mncu THANK YOU! Your solution worked for me.

1. Basically had to go into Device Manager
2. Find the wherever the dongle was listed as or listed under some name
3. Update driver, and pick from a list of available driver. By default it will be set as a "Generic Bluetooth Radio", but you need to select "Generic Bluetooth Adapter"

Connecting to bluetooth devices natively is just soo much better and a seamless process to switch devices rather than use the TP-Link driver software.

Thanks again for the help

@jrmistry That's interesting the 2004 bloke your BT as well. It took out the built in setup, so I tried the external dongle to see what would happen. It didn't work either. The dongle was listed in the printers and devices section with e picture of a headset (as is seen in this thread), however, I was unable to find it listed in the actual device manager., therefore I was unable to update it or choose a different driver.

I had this problem, but found a solution that I hadn't seen explained in full anywhere else (although the idea of updating the driver that some people have mentioned was the clue that let me find the solution).

If you're using Windows 10 with a UB400 Bluetooth adaptor and Windows isn't recognising it:

1. Go to the Windows Device Manager
2. Look at the Universal Serial Bus controllers
3. Right-click “CSR Bluecore Bluetooth" and select “Update driver”
4. Click on “Browse my computer for driver software”
5. Click on “Let me pick from a list of available drivers on my computer”
6. Pick “Generic Bluetooth Adaptor” in place of “CSR Bluecore Bluetooth”
7. Click “next”

And you're done!

@JaydenH 

None of the solutions here worked for me. 

The only one that worked, after googling a bit, is this one:

In Device Manager > Universal Serial Bus Devices > "CSR Bluecore Bluetooth":

1. right click on it, select "Update Driver"
2. Select "Browse my computer.."
3. Select "Choose from a list of available drivers..."
4. Choose "Generic Bluetooth Adapter".
5. A Bluetooth section will appear in the device manager.
6. You will be prompted to restart for completion.

And that's it! The bluetooth icon will be available to pair with any other device.

@JaydenH, I had similar issues and i had to go to Add or remove program and remove CSR Bluetooth Harmony Stack, then scan for hardware changes in device manager and suddenly everything started appearing again. Also check, ctrl + r, type services.msc and see if  BluetoothSupportService is running otherwise restart the service and reboot. Hope this helps.

Win10, version 2004

My issue was that the Add bluetooth or other device button was non-functional in Bluetooth Settings. The botton would blink, but nothing ever happened.

My solution was 

1. Go to Control panel > Network and Internet > Network and Sharing Center

2. Click on Change Adapter Settings. Then right click on the Bluetooth network > Properties

3. Select the Bluetooth tab. Click on Manager Bluetooth Personal Area Network Devices

4. Click on Add a device and the search will start. Enable search on your device (e.g., headset) and they will pair.

@JaydenH If it is not recognized, please download and install the Bluetooth driver manually from the official website. Try to insert UB400/ UB4A into a different USB port on your computer. For Windows XP/7, try to restart the computer after installing the driver.

@Tony Thank you so much! Your solution soved my issue :)

@JaydenH A little bit too late, but I run into the same problem: my computer has a faulty integrated BT adapter, and Windows would not recognize the UB400 I got as a replacement. The UB400 will work only after you disable the default adapter. Try disabling the default adapter and rebooting your machine.