Angelica,
Disconnect your machine from the power supply.
Cut the treads between the cloth and where the needle passes thrugh the slots in the table below the needle with scissors.
Undo the needle thumbscrew obove the needle, remove needle. then undo the box beneath your needle area, it's the bit you lift and undo to unload/load the bobbin with the cotton on, you will find two finger nuts holding the bobbin area together, undo these, noticing how they fit first, when you have undone these, your bobbin area will fall out into your hand, check how they wre fitted so you can put them back correctly, pull out any fluff and accumalated threads, clean it out finally with a small stiff clean paint brush, or better still use a hoover with is crevice nozzle on, both is better, even a tiny bit of fluff can divert the action of the needle and thread in the bobbin area, and begin to jam your machine, reassemble the parts you removed in the above instructions, check that they all seem to be in their right places, you can tell if they are not because they will be so out of place they will immediately snag with each other, and making sure they turn smoothly by moving the wheel you use to start your machine off when sowing normally. replace the bobbin, and refit the needle and turn on the power, and that should fix it, sowing machines are quite contrary and need to be cleaned out as shown above on a regular basis, I suggest you make it a habit to hoover the parts described above every time you use your machine, make sure small parts are removed before you hoover, otherwise you will find them in your hoover dust bag!!!you will then have trouble free sowing in future, you should have had a small brush in the tools when you bought the machine, and that is made to do just what I have detailed above, and it only take 2 or 3 minutes to do before you put your bobbin in place, but your problems will go away and let you make a good job of you projects.
I hope tis helps, if not write me back.
Stanley, October 2004