I noticed sometimes when you mess with a machine too much, occasionally they'll get jammed.
Happened to a generator once, and it would refuse to burn anything, no matter how much power was in the system it was connected to.
Happened to my mass fabricator too, have to rebuild it 
What I did:
Kept putting in scrap as it ate it, as I had several stacks.
What happened: It just stopped working, no sound, no progress, nothing.
What I tried to do to fix it:
Removed it from the power source, ran it on a lapotron crystal, no effect.
Removed it entirely and put it back down, no effect.
Replaced the wiring in case that was bugged, no effect.
Damnit.