few causes off thread not getting picked up,i start with simple things,insert new needle,make sure needle eye face forward and cut out at back,check lower and upper tension.if this does not work it could be timing.remove bobbin case and needle plate you have clear view off hook and needle.turn handwheel towards you observe when needle is going upwards the hook point must be just above the needle eye.you can also try moving needle up or down in needle bar to see if timing could be the problem.there are also a few places on internet that will show you timing procedure
johan
September 2013