On top of the solenoid there is a relief screw...happens to use if forklifts get stuck in the air... Unscrew until some fluid comes out and the airlock or whatever let's the forks down
Check the MCV, inlet and/or outlet section (I dont know exactly), you have an relief valve and somewhere the measuring point. Check the pressure, something 180-200 bar is enought, If the pressure is lower, adjust it. If not working, change the hyd. pump.