Are you sure the bobbin size is correct for your machine? Is your bobbin suppossed to be flat or have a concave to top and bottom? Not alll bobbins are alike nor can one that says Universal fit all machines.
All it takes to mess up is a small stray thread somewhere in the bobbin housing.
Take a breather, walk away, and after a bit with no interuptions, get out your manual and follow it step by step from the beginning. Sometimes we can forget one little step or we get careless and think we have something threaded right and really we don't. Good luck.