I believe these are open center valves which means that flow goes through the valve and back to the reservoir when the valve is in neutral. When activated, instead of the fluid going to the reservoir, it goes to whatever is being hydraulically driven. Usually with open center, the valves are all in series allowing for any valve to be activated at any time.
Closed center is usually used on high performance systems so when in the neutral position, the fluid doesn't go to the reservoir but to an accumulator.
Check the screw knob under your seat and make sure it hasn't been closed off.