Check to be sure the needle is installed right.Rethread using same thread in top & bottom.Have you changed any settings?
I had a funny sound,then no sew & I'd left it in bobbin winding mode. My mistake! Have you cleaned the bobbin area? Never hurts to do it again.Read your manual. Hope you can find the problem.

I had the same trouble a few years ago and found that all the bobbins i had at the time were slightly warped. I couldn't even tell unless under a mag light.

I found a picture of the bobbin I am supposed to use in this machine and matched it up to the bobbins I was using and I had the wrong one in. I found one that was right and tried that and now the machine stitches fine. In straight stitch anyway. It still does not zig zag right, but I can live with that. I am not sure machine I will use in the frame. The Kenmore has a cabinet, so I may find another one here that works as well. Throat size is my first concideration. And that it stitches well. I have several to choose from. I need to get one of my vintage machines ready and use that maybe, although they are so heavy.

Glad you worked it out.Know how frustrating it can be to have a good machine throw fits :-)