The motor capacitor may be dead, or a bearing seized. Call a technician.
This is the most common mistake homeowners make. A standard cup plunger creates a vacuum. If you apply that pressure to a Saniflo, you can blow the seals inside the macerator unit, causing permanent leaks or breaking the internal mechanism. how to unblock a saniflo toilet
Before we look at how to fix it, we need to cover what to do. The motor capacitor may be dead, or a bearing seized