Usually when there's a mess on the bottom it has to do with some tension problem on top. If cleaning, re-threading and making sure the tension dial is set at "normal", doesn't work, it could be under the needle plate. Unscrew the screws and take a look at your plastic bobbin case. Is is scarred up? Is it sitting in it's proper position? Is the area under the needle plate packed with lint? Is there a broken pin under the bobbin case? Is the hook damaged? If it has a plastic hook, throw it away and buy another machine.