[Sewing] Serger not working?

[Kelly]

Hey folks. The serger doesn't seem to be knitting together all of its
threads. I can't figure out what's wrong. The three main threads
appear to be threaded correctly. I can't find the end of the very
bottom one, but as far as I can see it looks threaded right. But when
I sew on test scraps it's not managing the crossover stitch.

Thoughts? Anyone around? I'll try to make do with straight stitches...

-Kelly