Civilian Target

Hi all,

Shock and horror, I have a Half-Life question. I finally got around to
playing Episode 2 this weekend, and I'm stuck. I just killed the
guardian, outside by the ant-lion column things, and the forces are
heading north to the forest. The electric guy has started a generator to
an outside elevator thingy, and himself and Alex are now waiting for me
to do something. At the top of the elevator shaft, there's a tunnel
which I guess takes me onwards

The problem is, I can't figure out what to do. There's a door at the top
that it looks like I need to get to, a hook and an elevator. I can open
the top of the elevator, but if I go inside, I get stuck and have to
reload the game. There's a hook hanging for the top, maybe I could
attach it to the elevator, but my gravity gun won't budge it. There's no
obvious boxes or things I can put together to climb up.

What should I do?

Civilian_Target