sewing machine probs

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sooo i used to have a problem with my lower bobbin thread, but that was solved forever ago. NOW it's doing it again. i've rethreaded the bobbin, switched it over and back again, and it just won't catch. i bought new needles earlier and it's not that either. i've tried different tension settings.. nope. now i'm noticing that the needle isn't pulling the top thread at all, only sewing the slack between it and just pumping up and down after the slack is gone. i don't know what to do! i really hope this is a simple fix! i really don't want to have to take it somewhere to get it repaired.

i've even opened up the bottom where the bobbin is and it's not dusty and there isn't any dust or fabric stuck anywhere. helppp!!