That insipid computer Xerxes has shut down the elevator as well. You can transfer power at the engine core on Deck 1, which will get the elevator up and running again. But you can't use the elevator to get down there. Wait... there's some kind of maintenance access right on this hallway. You can use it to reach deck one. However, it's locked and Xerxes is hiding the passcode from me. Dr. Watts should have the code. He's probably in the Crew sub-section. Grassi has the key to get in there, but he's in the Medical sub-section, probably near the biopsy lab. Now get to the Medical sub-section and find Grassi.