IS the shop you got it from nearby? I think I would try calling them. Does it stitch ok when not embroidering?

I purchased online. And no, I did not tried to sew yet just embroidering.

When my machine (which is a Viking/Husqvarna Sewing/embroidery machine) did what yours did, I had put the bobbin in upside down.

In looking for an embroidery machine figure out what do you want to make? Check out a lot of the embroidery websites and check out the sizes of the pattern you like. I know there are programs out there that will divide a design into sections but you may just want to get a machine with a larger hoop. My friend has the Brother 770 which the largest hoop is 5x7 and she loves it. She wanted the stand alone embroidery machine. I have the Viking Topaz 20 which the largest hoop is 200mm x 260 mm, roughly 8 x 11. My machine will use the magnetic hoops - which are nice for fabric you don't want to hoop. I use a lot of Accuquilt applique designs that need an 8 x 8, hoop. My friend uses my machine when she need something larger. My machine is a sewing/embroidery machine. I take it with me to my friend's home in AZ. I have used it to sew and embroider. But my main sewing machine at home is the Janome MC6600P. it"s now 10 years old and the man that services it said it should last another 10 at least. Hopefully you live where there are dealers you can go test drive a few machines before making a decision. I highly recommend taking lessons on the machine you buy. There are so many details to learn and the classes are do beneficial.

It doesn't matter which side you put bobbin in. I checked the bobbin case for scratches - nothing, changed the bobbin. Changer tension on the lower thread nothing.

it matters how the thread comes off the bobbin there is correct way

When you put the bobbin in, and pull on the thread, does the bobbin rotate clockwise or counterclockwise? Check your manual to see what way it is supposed to rotate. It really does make a difference. Mine will not sew and knots up if the bobbin is rotating the wrong way. I would take the manual, remove all the threading, and follow the manual step by step to rethread it. I also would just try doing some sewing first. As you have changed the tension settings, you may need to readjust them. Look for some you tubes on how to adjust tension on your machine. Bernette.com also has tutorials that are very helpful

I set up machine for sewing and it is sewing perfectly. So it's something to do with bobin case, I think. Ilook for the scratches on it but could not see anything. I do not have a clue what else could be.

Is it a different bobbin case for the embroidery? What thread and bobbin thread are you using? What kind of needle? There were some videos out there on how to set up your Bernina 79 for embroidery. There is a learning curve for a new machine and embroidery. Do you have any friends nearby that do embroidery? I don't have a bernette but I do have a Bernina.

Yes there is a different bobbin case for embroidery. When I started at first to embroider I set up the machine as required and it was embroidering perfect. But when I started the next embroidery it start messing up. So maby it damaged the bobbin case. I do not have anyone who does embroidery that I could ask for advice.