Although there are a few things that can cause this, the most common cause of this problem is that the upper thread is not threaded correctly. Try rethreading the top of your machine, while the presser foot is raised off the fabric. Make sure you pull the thread snugly while going over and under the guides, so it gets pulled in properly. Other things include bad or improper thread so you might want to try a different spool.
This is the opposite of the previous question. Normally this means that the bobbin is not threaded correctly. Make sure the thread is pulled into the slot and has stayed in. If it is unthreading while you sew this usually means you put the bobbin in upside down (check with your instruction book) or that you may be turning the hand wheel backwards.
When you flip the drop feed button the feed dogs go down immediately, but flipping the button back seems to have no affect. This is normal, the feed will come back up when taking the first stitch, so just make sure the button is in the up position and start sewing.
Breaking threads are often caused by bad needles or bad thread, but if it is the lower looper thread that keeps breaking it may be the order in which things are being threaded. The rule is loopers must be threaded before the needles. To rethread the lower looper we must cut the needle threads so we can thread the needles last.
