For some reason, the bluetooth adaptor failed to work on my Windows machine. Get it back by updating the drivers. Now my keyboard that was paired before is not recognized and when I try to pair, Windows keep prompting me for a PIN which I don’t have (it pops up once but I don’t get the chance to write it down).
Again, Google around for solution and spot the below.
I found solution for my keyboard... When it pops out to put PIN just tipe 4 digit number and click connect and then press the same 4 digit PIN code on your bluetooth keyboard and press enter/return
Excellent and now back on it typing!