Check two things: power and the start sequence. First, verify the power cord is firmly plugged into a 120V grounded outlet. It needs to be a dedicated outlet—no other appliances on the same circuit. Second, you must select both a time and a temperature before the unit will start. Just plugging it in isn't enough. Press the control knob to set your time and temp, then press it again to begin cooking.
If that didn't work, unplug it and inspect the cord and plug for damage. Do not operate it if they're damaged. Also, ensure you're not using an extension cord; it requires the short cord plugged directly into the wall.
Heads up: If the unit overheated, an internal protection system may have shut it off. Unplug it, let it cool for at least 30 minutes, then try again.