You have to start from #1. Get your bobbin tension right. There are videos on the HQ site to help if you do not know how to do that.
I use only bottomline prewounds and they fall quickly into the palm of my hand when holding the bobbin up.....looser is better than tighter.
Use a thread you KNOW works on top and bottom for now. Take out the thread and rethread the whole machine--make sure the needle is in the right way. Make sure the thread is seated in the tension disks. Tighten it all the way------then back off about 7 full turns. You are now back to factory set.
Now try stitching and see how it goes.