Sounds like low fluid to me as well. If the pump is running and things are not moving, there is no pressure. Simple as that.

Try releasing the pressure (or waiting ten minutes and it will release on it's own - or disconnect the battery and it will release instantly) and raise the lid manually. You can then look down in the driver's side rear wheel well and see the fluid in the tank - it should be well over 1/2 full, I believe 3/4 full when the system is at rest.

But if the fluid IS low, you have it leaking somewhere. Perhaps by raising the lid you will see where the leak is, as all lines and cylinders are pretty much visible with the lid raised.

Manual raising of the top is described in the owner's manual. What they do NOT tell you, I do, right here: