The things I've done:
Broke the boxes jamming the pump.
Went up the stairs and activated the power generator.
Flipped the switch thing where the dying body guard is to move the train track where Gargantua is.
I've killed and explored everything, besides Gargantua, but that door won't open.
I'm on the power up level in Half-Life 1, and I'm trying to get the Gargantua to follow me through the door so I can press the button to kill it, but that door isn't open...
I tried searching, but didn't find many results. Can someone help me?