Stuck on first level

[trolly]

Hey all, I just installed the game and on the very first level, I cannot advance past the point of taking the sentry's supply key-there looks to be an elevator or something but I cannot get it it to activate-do I use this key I just got -I have tried this also but nothing happens-thanks in advance for any help.

 

Trolly

[Sister3]

Press the letter e to activate any switch or elevator