Dumb question first. How do you know it will go up if it doesn't go down
And yes, hopefully the safety lever (stop) is dissengaged..
The system is hydraulically operated. I am pretty sure that your tilt pump motor has a two wire connector. If 2 wires and not three, the pump works by reversing direction of rotation depending on the polarity of the leads.
When you say you hear it trying to work, are you hearing the actual pump running or just a click? There is relay that controls pump rotation direction and it can go bad for up or down. If it is bad, you won't hear the pump pumping. There are also check valves in the pump assembly and if they get stuck or leak, one of two things happens depending on how bad they leak of stick. You may not have the flow of fluid to pull the pistons in and lower the motor. You may not have enough flow to raise the motor. If the leak is not gigantic the tilt position may change over time (The motor will drop down from a raises position).
A few things, while pushing the down button ( and confirming that the pump is running) try pushing down on the motor. It may lower.
If not, try loosening the relief plug as mentioned and see if the motor drops.
Don't stand under it or have your fingers anywhere where they could get pinched if the motor suddenly drops.
Note that the leaks I mentioned are internal and are not visible on the outside.
And of course, check the fluid level in the reservoir. I don't think that is the problem but who knows.