This may sound over simplistic in a day and age when there is a control board for everything. But, anyway.
You may have done this, but I would trace the water, like you would trace electricity.
Verify good water flow at the inlet valve to the refrigerator, run some in a glass. Then disconnect the next hose and actuate the valve through the dispenser to see if it goes through the valve. Check for clogged water filter, frozen water tank, or lines etc. Hope this helps. Let us know what you find.