Everything I tried from online wasn't working for me to resolve the issue of Bluetooth connection.
Here is what worked for me.
1. Went to Control panel and uninstalled Realtek Audio Driver
2. Restarted my machine.
3. Windows asked me to restart again - I think this time it was to finish installing the newer version of the driver. Hence I see today's date after the restart.
4. Made sure the Aux Cable wasn't hooked up to my machine.
5. Turned on the Bose Speaker and pressed the Bluetooth button until the light started blinking
6. Went to Bluetooth & other devices and click on the + button to Add Bluetooth or other devices
7. This time it showed my Bose speaker on the Audio Section instead of other devices section.
And there it worked.
If it is still NOT working go to Sound setting from the control panel and make your Bose Speaker the default device by clicking on the <Set Default> button below.
Hope this works out for you and it did for me.