Diagnosis
This is almost always a tripped thermal overload protector or a power supply issue, not a major failure. These units have built-in safety cut-offs.
How to Fix It
Unplug it from the wall. Wait a full 10 minutes. This lets any internal thermal fuses reset. While it's unplugged, check your wall outlet with another device to make sure you didn't blow a circuit breaker. After 10 minutes, plug it directly into a wall outlet (not a power strip or extension cord) and try turning it on.
If That Didn't Work
If it's still completely dead, the internal fuse on the control board might be blown. This is usually a small, clear-windowed fuse you can see on the main circuit board inside the housing. Replacing it requires disassembly and matching the fuse's amp/volt rating exactly.
Heads Up
These are power-hungry appliances. Always plug them directly into a dedicated outlet. Using an extension cord, especially an undersized one, can cause voltage drop that overheats the motor and trips the internal protector.