I have an Imagine serger. so let's see....it has two threads on the left for the needles. The next spool is for the upper looper and the last one is for the lower looper. If the stitches are not happening, take a look at the threads. The chances are that one or more threads may have skipped or did not go through on one or more points on the machine. I suspect it is one of the needle threads. Since the upper and lower looper threads are automatically threaded through the serger, the needle threads may be the cause due to the fact they are threaded manually.
If this is not a problem, a trip to the BabyLock dealer is a good way to go.