Thank you for your question.
I am sorry that you are having a problem with your serger. They can be a little tricky to keep in tune.
With out the brand and model number I will only be able to give you a general answer.
In replacing the needle,there usually is front and back to the needle. Make sure you have it installed correctly.
As you said that you broke a needle,this may case the upper and lower looper to become mis-aligned and you may have to take it in to be re-timed, or re-aligned. In some cases the looper can get hair line cracks at the place where you put the thread through.
The thread tensioning is very critical on sergers,I would suggest to start over with all the tensions at the base setting as outlined in the owners manual.
If this does not get your serger stitching again, it will need to be serviced. Do to the complexity of the timing on sergers the service locations have special timing tools to re-set your serger.
If you do not feel confident repairing this problem yourself, then you can have it repaired by a Sears technician. Here is a link that will provide the nearest drop-off locations:
Sears Home Services
I hope this information was of some help. If you could include the model and brand I may be of more help to get your serger working.
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