Have you tried adjusting the tension? Everything you have done so far is perfect and a great way to start. I know adjusting the tension can be scary. Start by examining what it looks like on the bottom when you try to sew. If there is a loopy mess it is usually the top tension. if the loops are on the top it could be the bottom tension. If your machine has been working up until now it may need a good cleaning check for heavy lint in your bobbin casing and other places that can collect lint. If these things don't help it could need a trip to be tuned up and a good service call.