Are you using machine embroidery thread top and bottom? Madeira or something similar with a silky sheen. Always, same thread brand and weight top and bottom although you may want different colours for some tasks.
Also you will need stitch and tear or some other suitable stabiliser under the fabric to give it body and support during the stitching.
Have you embroidered successfully on this machine in the past and this problem has now occured?
If so, I would take it back to the dealer and ask him to test sew a design with it and see if he can get a good result out of it.
If you are new to machine embroidery then perhaps visit
http://sewing.about.com/od/machineembroiderytips/Machine_Embroidery_Tips_Information.htm for lots of help and advice on machine embroidery.
Also I'd suggest that you revisit how you wind the bobbin - check your manual or there is more on this on sewingabout.com as it is essential to get a good smooth wound bobbin with no jerks or unevenness - you don't want the thread stretched unevenly onto the bobbin as it will relax unevenly when stitched out.
Then revisit bobbin threading into tension device, bobbin thread showing on top of fabric is usually indicative that there is insufficient tension on the bobbin thread, check that it is fully into tension and bobbin is in the right way, you always want the thread to come of the bobbin in a "V" shape, and bobbin should turn anticlockwise as you pull thread from it usually (but please check machine manual for specific threading for this machine, there is always the one exception).
Finally, does your machine have tension adjusments on the bobbin case? some have a little dial that will allow you to make small adjusments, although usually not necesary, adjusting the top tension is usually all that is needed.
I hope this is of assistance to you, obviously if you have tried all the above already, then I'd go back to the dealer and see if he can get a better result for you.