Did you try to raise the 3pt with the weight on it? I don't think you indicated that you did. You just said that you lowered it and then put weight on it. Frankly, the three-point should be able to lift the front end of the tractor up in the air before it breaks, under most circumstances. So let's say you put enough weight on the three-point to bend an arm or something. My thought is that the front end would lift up until the weight touched the ground. No damage done.
If you tried to raise the three-point with excessive weight on it, then as Baby Grand pointed out, the hydraulic system should go into relief. If you continued to try to raise it, eventually they hydraulic pump would overheat and be damaged, similar to if you were dead-heading a pump. To do this, you would have to put weight on the three-point, then raise the position lever, then just leave it there while the three-point failed to raise and the pump whined. But again, under most circumstances, even then, I would expect the front end of the tractor to go up rather than everything to sit stationary.
At least that's my amateur's interpretation. Do the other hydraulics on the tractor work? Power steering? Loader?