Mac, until Syd can get here to help you out, I'll post a piece of the most complete walkthrough that I found on this part. I wonder if the solution doesn't lie in going back a second time to get the scarf... SPOILER
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ELLEN: Use the door in the pyramid front. Walk to the opening, then to the passageway. Push the fourth monitor. Use the wiring. Walk back to the Atrium. Push the electronic bricks. Use the secret passage. Look at the sarcophagus. Use it. Push the keypad. Look at the statue. Talk to the statue. Use the following dialogue choices:
1.} "Who are you?"
2.} "Why won't you let me use the keypad?"
3.} "I am not a grave robber!"
4.} "I won't steal anything. I just need to know if you can tell me where AM's original brain components are."
5.} "Answer me this: who's sealed up in the scary sarcophagus?"
6.} "Can the sarcophagus lid be opened?" 7.} "Okay, so what's the access code?"
8.} "Who do you serve?"
9.} "Who is the master? Is it AM?"
10.} "You'll never get laid with that line of stuff, Anubis. Take care of your boring self. Bye now."
Go to the passage into the Embalming Room. Take the yellow fabric. Walk BACK into the Embalming Room (after you run out screaming), and take the
yellow fabric again.