You need to do some bite inhibition training pronto.
Ian Dunbar's siteis a good place to start.
Beyond yelping, remove yourself from the room and the dog.
You're probably fully aware that your lovely Border Collie has strong herding instincts. One of the tools that they use in herding is nipping and biting. It will take a fair bit of consistent conditioning but it will pay off.
If it does get worse, look for a professional trainer to help you.