Could be some antioxide compound. The first thing to do is remove the load wire (the black typically) wire going to the breaker and then see if you can reset it. If you can, you've likely got a ground fault somewhere. If you can't then the breaker is probably defective.

If you can reset the breaker, make sure that the white wire from the circuit is connected to the appropriate screw on the breaker and for most GFCI breakers the white (often coiled) pigtail is connected to the grounded bus bar.

Once you do that you'll need to divide and conquer on the circuits involved. Disconnect all the loads. Look in boxes for things like ground and neutrals possibly touching or wires touching another circuit.