You say "if i put water in bottom of dishwasher it works perfect" so your cause is water input. Dishwashers fill by time so anything that limits the flow will cause a low fill.
Low water level will cause the pump to suck air (cavitate), this air prevents the pump from developing any decent pressure.
Remove the kick plate
Shut off the water supply
Remove the fill valve
Have a pan ready to catch the water
On the input side there will be a screen filter
There is a good chance it is partially clogged
Sometimes you have to disassemble the valve to clean it properly
Make sure to mark the valve and bracket so you get it back together right
Usually 4 screws hold the mounting bracket to the plastic valve body
Remove these to get easier access to the filter
When reassembling make sure the rubber Oring is properly seated
Note: Do not run the unit without a screen. It prevents junk from getting into the valve which could cause the valve to stay open and flood the kitchen.
Could also be your water pressure has dropped for some reason, valve not opening fully, valve not being activated long enough by the timer but usually it is the above.
Do not know if you do this but you may want to drain some water out of the hot water tank bottom. Let it run till you get clear water. Helps cut down on gunk in the lines and also makes the tank more efficient. | 
Not enough pressure 
