BREAKING NEEDLES? Make sure your needles are correctly offset?
Flat back of needle parallel to back of machine?
Schmetz 90/14 size Universal needles come loaded in the serger from the factory, other sizes of needles work, but not larger 90/14, both left and right are same exact size? (don't laugh, people do all kinds of things)
Do not attempt to use Jeans or Denim needles in the serger.
Use the right needle for the right type and weight of fabric:
Universal Needles are for use with woven fabrics like quilting cottons, etc.
Ball-point needles, stretch needles and jersey needles are used with knit fabrics.
You can download the Schmetz Needle app for handy use in your Android phone or tablet https://play.google.com/store/apps/details?id=com.schmetz.needle
Bulk needles can be purchased via Amazon
Other things to check - unplug machine (so to avoid accidentally serging yourself) and handwalk the flywheel on the right side of the machine toward you - and listen carefully for any clicking rubbing noises as you walk it through a few stitch sequences.
If something is bent - you will distinctly hear it. Save this post for future reference, paste it in your Serger Journal. http://www.sewinginthebarn.com/journaling.html