Holmes HM5700 Won't reset. Screen comes up with reset and starts counting down form 450

Hard water will build up on the rubber plunger casket and the beveled edge were the plunger seats in the cap, if you clean both pieces it will seat it self again

I dont see any other way to fix other than purchase another cap...
I ordered 2 replacement caps from here they were the cheapest tat I found http://www.jardenstore.com/productdetails.aspx?BrandId=494&pid=1783 but they seem to be out of stock at the moment These http://www.appliancefactoryparts.com/humidifiers/holmes/holmes-water-tanks.html are 3 dollars more here hope this helps

I ordered 2 replacement caps from here they were the cheapest tat I found http://www.jardenstore.com/productdetails.aspx?BrandId=494&pid=1783 but they seem to be out of stock at the moment These http://www.appliancefactoryparts.com/humidifiers/holmes/holmes-water-tanks.html are 3 dollars more here hope this helps

You might need to clean around the heating element...
we have very hard water and calcium builds up on and around the heating element and all the surrounding parts. I take it apart and pour CPR around the element and scrub with a brush .. once you get it clean it should stay running.

If you can see the mist, then, it is working. The outlet
port of your humidifier could be closed/stucked up/clogged. Please check this the outlet port.

This page has 18 pdf user manuals they are only 1-2 pages each open them in adobe reader till you find the one you need wish i could be more help
http://www.holmesproducts.com/Manuals.aspx

turn knob to reset....leave 15 minutes and then turn on

According to Holmes, one of the causes of the Reset light staying on is scale buildup on the heating element.

Remove Scale: Allow to cool before maintenance.
1. Repeat steps 1-5 in the Daily Maintenance section.
2. Clean the base by partially filling the base with one
8-oz cup of undiluted white vinegar. Let solution stand
20 minutes, cleaning all interior surfaces with a soft
brush. Dampen a cloth with undiluted white vinegar
and wipe out entire base to remove scale.
3. Rinse with clean warm water to remove scale and the
white vinegar solution before beginning to disinfect
the tank.
4. Wipe the heating element clean with a soft cloth after
it has had chance to cool.

If the scale has really built up it might take longer than 20 mins for the vinegar to get rid of it and you might need to refresh with new vinegar.

Your Manual can be found at this link:
http://www.holmesproducts.com/Manuals/Holmes/HM5250-UC_English.pdf

Good Luck.

possibly calcium or other deposits from the type of water you are using in the unit..........

Per the operators manual you have to reset it. 1. Unplug the unit
2. Remove and refill the water tank, being sure to follow the Daily
Maintenance Instructions. Replace the tank onto the base.
3. Wait 5 minutes for the Automatic Shut-Off to reset.
4. After the 5 minutes, plug in the unit and turn the unit on to HIGH
(HI). The RESET light should now be off (if not repeat steps 1 through
3). In about 2-3 minutes, the humidifier will begin to produce
moisture.