1) The needle is not raised to the highest position A) Raise to the highest position for mechanical machines position the line on the handwheel to the top(refer to upper threading in your manual, for electronic machines press the needle position button so that the needle returns to the top.
2) The needle is not installed correctly A) ensure the needle is fully inserted into the needle bar clamp before you tighten the screw and the flat part of the needle is to the back, please note singer and butterfly needles are not compatible, brother recommend Organ or Schmetz needles, 11/75 is the smallest needle you can use with the needle threader.
3) The hook of the needle threader is bent and does not pass through the eye of the needle A) Please contact your dealer for support or use the dealer locator to find your nearest repair centre.  Please note needle threaders are not covered under warranty.