Take a deep breathe...Ok, A good first and often only step you need to take, is to totally unthread everything. Now go get your manual, good to the pages where it tells you how to thread the top thread and the bobbin, follow it step by step. I know that sounds simple but I can't tell the number of times I have been very frustrated and was convinced I was doing everything right only to find that sometimes, I had missed a thread guide, or the thread had somehow come out of where it is supposed to be. Some of the vikings have had a problem with the thread coming out of the take up lever at the top of the machine, When that happens it is no good! If that doesn't work, can you tell us more, like what threads are you using in the top and in the bobbin? How is it stitching terrible? Missing stitches, bobbin thread coming to the top? top thread making a nest on the bottom? As you have changed the tension, can you put it back where it was? Also, the bobbin area needs to cleaned frequently. I used to have a Viking D1, SE, and now a Topaz 40. My vikings have been good machine but I did have one plastic inner part wear out on my D1 after many years of use and it had to be replaced.