Serger thread cones are not designed to be used on a sewing machine. They are designed to be used on sergers as the thread stands that come on sergers are higher than the cones and allow them to unwind up to the top to feed through the serger thread stand guides.

This happened to me this morning so I turned everything off, unplugged, cleaned it (boy was it bad :() then I rethreaded the top and bobbin. Worked like a champ :)
Good luck.

Clean, change needle and check your tensions.

Yes, all of the above and my machine doesn't like rayon in the bobbin when the upper thread is cotton. Try those teflon thingys in the bobbin case, helps with "spider webs" too.

Can you tell more about the teflon thingys?

Wildyard, the teflon thingys are washers placed in the bobbin case before the bobbin is put in. The brand I have is "Magic Bobbin Washers" by Little Genie. I think it allows the bobbin to spin freely. I use it all the time now. It has helped keep the back of the machine quilted pieces looking good. There is a web address on the package, www.freemotionslider.com. I think I bought the product from either KQ, Clothilde or Nancy's Notions. Couldn't find it at my LQS's. The item is a little pricey but you get a lot of them and I would'nt want to sew anything without them.

Judi, thanks for the info.... learned my "something new" early today. Smiles and huggggggs!

Wildyard, you are most welcome, glad to help solve those "knotty" problems.

Yep, you have to hold the bobbin thread for the first few stitches. I've learned the hard way. But sometimes the problem is with the bobbin period. Not in properly, not wound up properly. Something. Bird's nests are bobbin problems.

yeah, mine were not occurring at the start, but randomly here and there across the back. It took me several times before I finally linked the badly pre-wound bobbin to the problem.