Stitches won't form???

This is a weird one I have never seen before in all my years sewing.
Bobbin is loaded.  Machine is threaded.  Bobbin thread comes up through the plate.  Everything looks right.  I am trying to sew, and everything is moving, but the stitches don't form in the fabric.  It's like the thread slips right through or something.

It was working fine, I changed thread and the bobbin and the needle...and then this happened.   I have tried taking everything out and putting it back in, but it's still happening.  I have no idea what to even try to look at.  The troubleshooting guide (it's a cheap Kenmore) is no help.

Any ideas?

Is your needle in correctly?  Ie: the front facing the front, back facing back?  Did someone play with your tension when you weren't looking (You know, those 'not me's' who live in many homes?)  Did you just buy new needles and they aren't the right fit for your machine. 

Frustrating isn't it, when you want to sew and can't go anywhere!  Wishing you the best.

Solved!  Posting in case someone else has this problem...

I was re-using a denim needle that I had recently used on another project.  Apparently, it must have been bent or something.  I took it out, replaced with a different needle, and everything was fine.  (I had tried re-inserting the needle before in case it had gone in wrong, but that hadn't solved it).

I hate to tell you this, but it sounds like you've popped a gear somewhere.  You don't say what kind of machine, but if it is one of the newer ones -- mechanical, electronic, or computerized -- chances are it has nylon gears.  After 8 or 9 years, those gears just give way. 

You need to bring your machine to a reliable sm mechanic.

Glad you solved it.