Here's a pic

Well, for me it was one of 2 things. I replaced the float switch and the solenoid that controlled the water coming into the system. After I did those two things, it worked GREAT!

Here's some of the stuff I tried before buying the parts... might be worth a shot for you.

In looking at other posts about this, I found the following potential solutions.

Problem 1: Your filter is clogged, causing the water to not be pulled up into the top blade
Solution 1: Clean the filter. Directions on this were posted as...

I'll see if I can help. It was last Fall when I did this but it is pretty easy.
Once you remove the arm, the plastic screw is turned opposite to remove, you'll need to remove the lower section of the water transfer pipe. This is the flat wide plastic pipe that delivers water to the upper sprayer. It snaps into the pump and if you remove the srew on the back wall of the washer the pipe will swing out of your way. No need to remove it completely. The big round screen is held in by three or four star screws. You'll need a star driver or a set screw driver. Once you remove those screws the screen should pop off. You may need to wedge it off with a screw driver or a dull knife. Once the screen is off the plastic housing (right in the front, covering the lower plastic screen is held in with one screw. I can not remember if it is also a star screw or not. I think it is in the front part of the screen. This screen snaps into place so you'll have to "unsnap" it. As I remember, it sort of folds forward into place. Once it is off you can see the metal "grinder" below and that's where all the good stuff clogging the water flow will be found!
I used a wet/dry shop vac to suck it all out.
Then the fun part, put it all back together!
Put a cup in the top rack right side up and give it 20 seconds of wash and it should be full!

****Be careful not to drop the screws into the motor!****

This is from the post located at:
Kenmore UltraWash Quiet Guard 3 Dishwasher no Longer Cleaning the Top Rack

Problem 2: The filter from your water intake valve is clogged and not enough water is filling into your dishwasher to create enough pressure to move the top blade. You'll know this pretty easy by starting your washer and waiting for the fill cycle to be done. Once it is done, open your washer and check the bottom to see if you have 1/4 inch of water down there.
Solution 2: Clean that filter. Directions for this are:

I had this problem as well and successfully cleaned out the bottom as instructed above. However, the problem still persisted. I determined that there was not enough water getting into the washer. There is a valve of some sort where the water intake connects. I shut down the power and turned off the water to the dishwasher...disconnected the water line. The piece that the water hose connects too is held in place by a small hex screw to the left of the piece. Then, I removed 4 small screws that held the piece together. This allowed the piece to separate and I could see a screen type deal inside that had a bunch of hard water gunk built up that seemed to be blocking the water flow. I removed the screen with my pliers and washed the gunk off in the sink. I replaced the screen and put everything back together. The washer was back to it's "like new" self! Hope this helps somebody!

This is from the post located at:
Kenmore UltraWash Quiet Guard 3 Dishwasher no Longer Cleaning the Top Rack Page 2

Problem 3: The water going into your dishwasher isn't hot enough.
Solution 3: One user posted that it should be 115 degrees. You'd have to get a thermometer of some sort to test this and then you'd just need to raise the temperature on your water heater. I don't remember where I saw this post and I'm not sure I believe it could cause the problem.

Problem 4: Your "float" is broken tricking your dishwasher into thinking it is full when it is not. This would have the same symptom as Problem 2.