You don't need a new machine or bobbin holder. If the machine was running fine until you changed thread, the problem is user error. Sorry. As a previous service person I would see this often. Do you have more than one machine? If so are you threading as if for the other machine? Do you have a manual? If so, please get it out and follow threading guide. I know we think after 4 years you would thread automatically, but sometimes we skip a step. Are you using a different brand of thread? Some machines do not like some threads. It's a mystery as to why one of my machine will not sew yLI thread. And some days it helps to walk away and return the next day and begin fresh. I hope you get it figured out. Now is no time to have machine issues. Good luck.