As the post above says make sure your phone is not in hide mode also you can try this.

Start pairing
then search for new devices using the phone
then type in your pass code which is a little credit card sized card with a 4 digit code on it.

Then you sould be good to go. You can have up to four phone paired at once every time you pair another knocks the first one off.

If this still dont work try another phone I would try and get a w800i or W810i as these seem to work better some people have had troubles pairing K750

Good luck