Serger won't run

I am guessing that you do hear the motor running... Not a Juki serger expert but...
Here are 3 things that you can check:
1. I have an ancient mammylok and a more modern semi-industrial singer and both have a housing on the side around the flywheel that can be unscrewed and removed so you can check the belt to see if it snapped, slipped or has just plain loosened. Inside my ancient serger, there are bolts that hold the wheel (which is connected to the flywheel by the belt) turned by the motor which can be loosened and pulled further out to adjust for a loosened belt.
2. On the base of every serger, there is a plate, if you turn it over, which will allow access to the internal mechanism of the machine for a more deep oiling and cleaning, so you can take a look to see how it looks in there.
3. My Bernina 830 Record (yes it is a sewing machine but hear me out), just stopped working one day, I thought it was the foot control, so ordered a new one. It arrived and still no motor...so off came the casing for the motor...I checked connections and made sure all were where they were supposed to be, put it back together and was dreading now having to order a motor, tried the motor again and it suddenly worked. I now have a spare foot control.

I love/hate my serger! Is thread stuck anywhere below? Bent needles? Are the needles in correctly and tightly? Is the machine greased? Unthread it, rethread. After all of this, it should work. Good luck. My simple old singer didn't do this but it wore out and the Viking is temperamental!

Don't force it. It sounds as if something is binding inside the machine. Take it in for professional service.

the best thing to do is take the machine in to have it checked.
sergers are nice & very useful, I have a babylock serger with the jet-air
looper threading systerm, and I use it alot when making clothes.
I even used my serger to serge the ends of fabric that I haven't used yet
so the ends won't fray.

if the machine is still under warrenty, take it back
if it's not under warrenty, take it to the place you bought it from & tell them

is there any smell to the machine?
it's possible that sewing the thick fabric could have caused the machine
to jump time
it would be a good idea to have it serviced at a sewing machine shop

there is something wrong with the machine, the feed dogs are what move the fabric, it could be many different thing, the motor, some part is worn or loose or broken, power cord, it needs to be serviced

Slacken the stop motion as if to wind a bobbin and press on the foot control, if the motor runs really fast then you have either thread stuck in the bobbin case area or you may need to oil the machine

Hi, On most of these newer machines they have a clutch that you engage to fill the bobins.
Please make sure that the clutch is disengaged for normal use. If this is all OK see that belt
is attached on motor.

pull the 4 bottom rubber feet out and remove screws hidden in holes. Lift main body of serger up. you will see the gears. Probably drive gear on motor shaft got hot and slid on motor shaft.