Why is my Keurig B70 Not Brewing?

My Keurig B70 will not brew even though the display says "Brewing." I've disassembled the unit to check the pump. When starting the unit the pump fills the water reservoir, then heats the water, then says "Ready To Brew." After pushing the "Brew" button the display says "Brewing," but nothing happens. Sometimes the pump comes on for a second or two and shuts off.