Water drains thru the vent

As far as draining the backed up water you may have to run a short cycle wash to help it. In California homes we have a by-pass vent which runs from the dishwasher drain hose up to a port in the kitchen sink. From there it is attached to the side port of a garbage disposer. In the event of a backwash the by-pass vent is high enough that it can't reach a level that wiould flow back into the dishwasher.

Theres a drain pump located at the bottom of the unit if you follow the hose from the pump then to the drain if your unit isnt draining you might have to call for service from a technician to have them change your drain pump. If the water is just sitting inside the unit and when u start the unit it should fill with water again.Also if you have a cancel function by pressing this you will make the unit drain if you dont hear anything when u press the cancel button you definetly need a pump

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Begin at your sink drain that the dishwasher drain hose connects to. Disconnect the hose and check both directions for anything plugging the connection.
Make sure the drain hose has not become "kinked"
(After you have emptied the water from the dishwasher) remove the lower spray arm and the filter in the sump area. Look for obstructions and remove all debris. Rinse the filter thoroughly and reassemble.
If you dishwasher has a timer on the front of the dishwasher that you can manually turn, start a quick cycle with no DW soap and empty.
Allow the water to run in for several seconds and then manually (slowly, gently) turn the timer knob until the DW should begin draining the DW. Listen closely for the sound of the pump motor running.Is water properly draining out of the dishwasher into the drain?
After you have done these things, please post back here and we can take the next steps. OK?

I would remove the drainhose from sink and try draining in to a pale.if it does not then you will need to remove drain hose and clean out.Also you may need to clean out all screens in pump just remove with torx screwdriver easy when you get into it

Try adding bicarb of soda/baking soda and vinegar in the detergent dispenser. Bicarb fizzes off hardened particles and vinegar strips off grease and aids rinsing.

Two things to consider....clean water or dirty water?
Clean water usually indicates the fill valve is not shutting off all the way and the fill valve is "weeping" water in all the time = new fill valve time!!
Dirty water usually is not a dishwasher problem but more of a plumbing issue. Often the sink drain that carries the sinks water outside is not fast enough and some of this sink water is backing up into the drain hose and filling up the dishwasher through the drain hose. The drain from the sink to outside needs attention as this type of a problem indicates a slow house drain for that sink.
The dishwasher drain line should be clamped to the top underneath part of the counter before entering the sink drain plumbing, this may help the water from coming back inside the dishwash
If the cycle doesn't complete, check these:

Water-heating cycle
Timer
Water-heating cycle Many dishwashers heat the wash and/or rinse water to a higher temperature, as the cycle calls for it. In these cycles, the dishwasher pauses after it has filled with water, waiting for the water to reach the pre-set temperature. What happens next, depends, as follows:

• On some units, the pause is timed and the unit continues after the allotted time.



• On others, the cycle can't continue until the water reaches the higher temperature. If you have this type of dishwasher and the water isn't being heated (say, because of a problem with the heating element or thermostat), after the unit stops at the heating cycle, it never continues. When you repair the heating-system problem, the "cycle problem" is fixed too.

Timer Timers don't often fail. But if every other part of the dishwasher seems to be working properly and the timer knob seems to be stuck in one place--doing one function continuously--the timer may be at fault. Dishwasher timers can't be repaired. If yours is defective, replace it. 

either
leaking valve - to check, turn water off and see if it still happens
or
if appliance is plumbed in to a spigot on the sink trap, then when you empty sink, some of the water finds its way into the dishwasher via the drain hose. to cure, take the drain hose as high as possible under the sink in a swan neck

If you have a fair amount of water in the bottom of most, if not all dishwashers then the problem solution involves one of several things to check.. First off.. is there a drain filter ( at the bottom of your dishwashere where the water gets drawn to the pump) that may be clogged up with waste material from the dishes? If that is clean... then the next thing I would check is for any kinks or clogs in the drain hose leading out to the drain system in your house.. ( many times the drain hose is attached to the side of the sink garbage disposal but it may have a direct attachement to the drain itself ( normally under the sink).. check that for obstructions.. and as a last resort.. if you do not see any kinks in that line.. you can detach it and cycle the dishwasher ( without dishes loaded) and run the dishwasher in a large bucket to see what kind of flow you get.. if you get a fairly good flow.. then you your pumping system is ok but your drain system in your home may be clogged ( improperly vented ) or restrictive to flow.. First things first.. check the drain screen, check the hose ... check the flow into a non restrictive bucket.. If the flow is weak.. then you may have a clogged or damaged pump.. Hope this helps you...

heres some few other simple checking & steps, that will guide you to the process...

1st
Remove the cover from the air gap at the top of the sink (usually a short chrome domed cylinder that sits at the back of the sink) and, using a wire, clean it. Also check the entire length of the drain hose for kinks and blockages, especially at the drain connection to the disposer or drain line.

2nd
Once the dishwasher is cool, shut off the power to it, and--if your dishwasher is made to allow this-- remove the strainer, located under the bottom spray arm at the base of the cabinet. Unscrew the hubcap, lift the spray arm off, and remove any clips that hold the strainer to get it out. Scrub it clean with a brush, then replace it.

3rd
Determine whether the sink trap or house drain line is clogged

4th
If it still doesn't drain properly, the drain hose may be clogged or the drain valve may need replacement. At this point, it's usually best to call a repair person. You can check the drain hose for obstructions, but this sometimes involves pulling the dishwasher out from under your counter to access the hose, disconnecting the hose at both ends, and flushing it out with a faucet or garden hose.

Let me know..

Thanks