You can get Necchi instruction manual from Necchi website: http://www.sewusa.com/Sewing_Machine_Manuals/Necchi_Sewing_Machines.htm
Makesure the needle is in the machine correctly- all the way up into the needlebar, make sure that it is threaded correctly, etc. If this all checks out ok,take the bobbin case out of the machine. There are two ears on either side ofthe bobbin case- turn the left one to the left and the right one to the right.Remove the silver ring, and inspect the piece of metal that the ring came off of(looks like a circle with the top cut off). You have to locate the hook whichis the piece that looks like a half moon inside the big round metal piece.Locate the tip of it, turn the hand wheel toward you until the needle is in thelowest position, at this point the tip of the hook should be flush with top ofthe left side of the cut off circle.
Checkwhether underneath thread is looping on the fabric. If so then you've mis-threadedthe top, probably haven't raised the presser foot when threading so you can getthe upper thread into the tension. You need to thread the upper part with thepresser foot up. (You can put it down to thread the needle.)
Not picking up thread can be several issues, like bobbin is miswound, bobbincase isn't snapped in properly, you're using the wrong type bobbin, machine isout of time, needle is bent or burred, machine is dirty and in need of dustbunny eviction and a little oil but most of the time the issue is once againmisthreading: sewing machine needles have a front and a back and they have tobe placed in the needle holder correctly.
In that case your manual is needed, take all the thread offthe machine (yes, spool off the spool pin, bobbin out of the bobbin case), pullthe needle plate and clean your machine thoroughly, using brush and vacuum (notcompressed air) and oiling per the instruction manual. Put it all backtogether, putting in a 80/12 needle, correctly oriented. Hang on to theneedle thread when you fetch up the bobbin thread.
Each and every seam you start is going to be done this way:
1) Pull the tail of the top and bobbin thread behind the presser foot
2) Put the work under the needle and use the hand wheel to lower the needleinto the work
3) Drop the presser foot
4) Holding the thread tails behind the foot, take a couple of stitches.
5) Drop the thread tails and sew normally.
Hope this will help you. Good Luck.