oooh, now I remember!
Yeah, I had trouble here too. I think you have to get the electrcity going or something like that. I remember you have to push some things around, or pick up a spare part?. Just look around the room, and interact with whatever you can.
I also seem to recall there being several "batches" or robots, that just keep coming as you kill them. I think there are like 4 or 5 groups, and after you kill them ALL, then you get the key. At first, I though they respawned infintely, but it turns out there is actually an end, its just really hard to kill them all and stay alive.