All of a sudden will not turn on. No lights on.

Can you say how it stopped working, please? Does 'it would not start' mean absolutely nothing happens or what, please?

The red water level light was on even though both tanks were full. The white float behind the filter WAS stuck to the bottom of the tank. I just moved it to its floating position and voila! it is working.

You didn't specify what brand/model of humidifier your using, but you can still try a couple of things. (Try the most logical first).
Try turning the control knob to the "test/reset" position & wait until the humidifier "on" light blinks; indicating it is resetting the timer & the change filter lamp will turn off.
I believe that you will need to do this while the furnace is calling for heat, if it isn't, turn up the thermostat and try it.

Mine is a SUL495 Filter Free unit and worked fine last year and the first couple of days recently, but I'm having the same issue, motor running , no mist, and trying to talk to someone @ in customer service today is a joke, I've cleaned everything but still no luck, I paid $40.00 for this unit in Jan. 2011 and have about two weeks until the warranty runs out, and the other wonderful thing is the nearest service center is about 50 miles away, I may wait until Monady to try to speak to someone, but I probably won't like the answers.

If you did not turn the unit OFF and unplug. it before changing the filter, do so now.Just repeat the process, but make sure the master ON/OFF Switch is OFF and the unit is unplugged before removing and replacing the filter. Be sure the filter is properly installed.Wait at least 5 minutes, before plugging the unit back in and Turning the Master ON/OFF Switch to ON. That should give the electronics time to rest themselves.

Hope this helps you.

If your humidifier is equipped with a Digital Humidifier Control with Water

Panel change indicator, after replacing the Water Panel, turn the control

knob to the "Test/Reset" position until the "Humidifier On" light blinks to

reset its timer. (Blower must be operating and HVAC calling for heat.) Be sure

to turn the control knob back to it's original setting. If the "Humidifier On"

light continues to blink, your humidifier is in Test mode. DO NOT LEAVE THE
CONTROL IN TEST MODE OR HUMIDIFIER WILL NOT OPERATE.

Turn the unit off and disconnect from the electrical
outlet.
2. Remove the tank from the housing.
3. Unlock the housing from the base by turning the lock
knob to the unlocked position.
4. Lift the housing straight up and place to the side.
5. Unlock the wick holder from the base by turning the lock
knob to the unlocked position.
6. Remove the wicks from the wick holder.
7. Follow the weekly cleaning instructions.
8. Insert new filters into the wick holder and lock the wick
holder back onto the base.
9. Replace the housing onto the base and lock it into place.
10. Fill the tank and place back into housing.
11. Repeat Operating Instructions.
It will take about 30 minutes for the humidifier to reach

Turn the control knob to the
“Test/Reset” position until the “Change
Water Panel” light blinks to reset the
water panel change indicator timer.
(Blower must be operating and furnace
calling for heat.) Be sure to turn the
control knob back to the prior setting when finished

clogged solonoid? clean filter and orifice

If you would like to buy a new tower without a tank, I will be happy to sell mine.