What is shown on the LCD display, and can you confirm the water level on the side is showing above minimum and below maximum?
This would suggest the pump has failed which is responsible for circulating the water, this is often caused when running the machine without any water, but since you have confirmed the water level is OK and its a new device, I would look to return the machine under manufacturers warranty (this is not user error).
The water tank should last for easily a days but have had them running for a few days, but the amount of water used depends on the settings and the environment (ambient humidity, water regulator setting and a fan speed to name a few).
In terms of what you can do other than amazon returns process, it may be the water sensor has got stuck where the unit was knocked in transit. You can have a go banging the lower part of the unit with your hand or lifting it up and dropping it from 2-3cm (not scientific I know) but may free the sensor - expect a puddle of water though.
There isnt really any other option than stripping it down, as it may be a lose cable to the pump, faulty sensor, faulty PCB, but to get to the circuit its fair job stripping it down.
If it cleared itself, it may have been a blocked pipe from debris which got into the tank which has freed itself, or the sensor has just come back to life. There isnt really anything more you can do as the unit isnt decided to be serviced by the customer (other than the honeycomb and grill).