Clean your machine.
Take the throat plates off, get a pair of tweezers and get all of the "fuzz" out of there. I think your feed dogs are not being allowed to raise up, consequently, no forward movement.
I have had this happen to me twice.
The first time it cost me $60 to have repairman do what I could have done for myself. He didn't tell me what had happened, but the second time, I had my suspicions.
So, I took the throat plate off, and almost missed the fuzz that was so impacted it looked like part of the machine and absolutely wouldn't come out without the tweezer, so felted that when it came out, it came out in bales! I couldn't even pull them apart with my fingers!
Clean your machine .... and, REALLY clean it. <wave>