The motor can develop a "dead" spot, when, if the motor stops on that spot, will not start again, unless you turn the motor from the outside with a straight slot screwdriver. You can see the slot on the end of your macerator.
Turn it with the macerator off, and then turn it on.
If this doesn't work, it could be a dead macerator, or maybe a fuse.
Our's actually shorted out, and got hot to the touch. So try feeling it. If so, it's toast.