The wrong loops are on the surface of the material that I've sewn

Lots of reasons for this. Tension, needle size, material and thread have to meet conditions for the material sewn. Make sure the thread is not old as thread deteriorates and can cause minute knots. Make sure you are threading the needle correctly. (I've been sewing for many years and sometimes DO NOT thread the needle correctly, it's easily done). Make sure the thread in the bobbin and top thread are the same. Make sure the needle is not bent or dull. Make sure that under the feedplate has no lint or bits of thread.
I hope this helps. :-)

Is the needle inserted correctly? It should not be difficult to change it. Here are some reasons for thread breaking. OLD thread, cheap thread, wrong thread for material and wrong needle size for material. Incorrect tension for material being sewn. Needle bent or too old. Hope this helps :-)

Lots of reasons for this. Must be same thread in bobbin and needle. Not old thread. Needle old/bent/blunt. Tension must be correct for the material sewn. Also correct thread, needle size for material sewn. Usually the bobbin never needs adjusting. Hope this helps.

Yes quality of thread could definitely affect sewing, as will a blunt/old/wrong size needle for the material used. Also must have same thread in bobbin and needle also corect thread and needle size for material sewn plus correct tension for that material too. Could be lint or tangled threads underneath needle plate too.

Looping and nesting on bottom side is usually a top thread tension too loose (or no tension). Always thread machine with needle up and presser foot up. See singer video https://www.youtube.com/watch?v=O7N4XaIV6ms


Less likely is bottom thread has escaped the bobbin case tension spring, but this usually results in a jammed hook.


If still having issues comment here so I may assist further.

Hi, could be the upper tension is incorrect. Clean out bobbin race from entanglement. Use a new needle and rethread. Make sure that the thread is new too, and that the upper tension, needle size and thread thickness are compatible with the thickness of material sewn.
Hope this helps. :-)

the looping on the bottom usually is a tension problem, the top & bottom tension are unequal usually fixed by adjusting the top tension.
some people that I've talked with have had success with changing to a different size needle ( depends what type of thread is being used).
when the machine is threaded the foot needs to be up ( this releases tension on the thread), when the foot is lowered it the tension is set on the thread. if the material being sewed is too thick it raises the foot too high & releases tension on the thread ( the material has to be really thick to do this).
if there a piece of thread or lint in or around the tensioner or bobbin area it could cause trouble.
other wise if you've tried everything you can think of, take it back th the store & have them try it & tell you what is wrong.

also this machine has bad reviews (i'll provide a link so you can read them), people having the same problems as you are. the newer singers just don't seem to be the same quality tha the older ones were.
all bad reviews
http://www.amazon.com/Singer-5400-60-stitch-Sewing-Machine/product-reviews/B007ZG9DTQ/ref=cm_cr_pr_btm_link_1?ie=UTF8&showViewpoints=0&sortBy=byRankDescending
mixed reviews
http://reviews.walmart.com/1336/20573406/singer-5400-sew-mate-60-stitch-sewing-machine-5400-reviews/reviews.htm

This is usually caused by the needle not being threaded correctly or wrong size needle or wrong thread for the material or old thread, or incorrect tension for the material being sewn.

Usually on a serger if loops too big you need to tighten top or bottom looper tension or both. The tighter the tension the smaller the loop. Also if you're not running the material straight with the knife it can make loops in places that although the same size as other loops it's covering less edge so the loops appear too large in places.

You will need to adjust the thread tension. If the threads loops are on the "down" side of the fabric being sewn, you will need to increase the upper thread tension ( or in some very rare cases, loosen the bobbin case tension ) Refer to your owners manual for how to make this adjustment. As this adjustment is relatively generic for most home machines you may be able to refer to a manual for a different type or brand of machine.