i'll add myself to the victim list. My Simplicity does that sometimes for no reason that makes sense. the singer, too. used to drive me NUTS!!! After getting sick of trying to get it working again, i'd put the [pick your favorite cuss-type word] thing aside, get out my backup machine and work on that for a few days. when i'd go back to the simplicity, it would work fine. go figure. i guess my machine has mood swings. LOL
purely by accident i discovered that if i take the top thread all the way out, put in a new needle and rethread the top (after unclogging the bobbin well, of course) it works again. i was surprised - and sorry - to read that none of those things helped you, Miranda, cause i dunno what else to suggest. except ... hmmmm .... i wonder .... are you using the size bobbin your machine likes best? all of mine prefer the old fashioned metal bobbins with the holes in them. (i don't know why. i've given up trying to find the answers to such cosmic mysteries. LOL)