L4400 steering problems

There are 4 basic components to that system.
Pump
Regulator
Steering controller
Steering cylinder

The Pump on that tractor is a 2 section pump, the section that runs the PS is not the same as the loader and three point.
So it's possible the pump is bad, crack the banjo fitting (in yellow) on the regulator output (part on top of the pump) that goes to the steering controller, if you get flow it's probably not the pump or the regulator.
Note: The other line that goes to it with the simple clamp is the return line, do not remove it for the test as it will suck air into the pump and make the test invalid.

Next if you have flow from the pump is to crack both fittings on the steering cylinder, with it running turn the steering wheel side to side, fluid should come out of one of each of the fitting when it's turned back and forth.

If you get fluid there it most likely has blow a seal in the ram and will need rebuilt, If not fluid flows then it most likely has a bad steering controller and will need rebuilt or replaced.