GE dishwasher arm not spinning - not enough pressure?

GE dishwasher, model GSD2000G00WW. Dishes not getting clean or wet. Opened door slightly, noticed lower spin arm not spinning, and the center "cone" just spitting water intermittently. Impeller making quite a bit of noise. I have disassembled pump,motor, and sump. Everything seems in working order, but why is there not nough force to lift that center "cone"sprayer and spin the arms?

Update. I just added more water as the unti was running, and the arms and everything spin fine??? Not enough water coming into the unit?