In the opening scene and the teaser trailer for that matter, when they zoom in on Sentinel's eye and it lights up, was that for shits and giggles to reveal the title or was he waking up?
I think it was also because the astronauts said "Everything is dead in here" and it was a foreshadow to the audience that not everything was dead.
I was actually wondering about this when I watched the movie one of these days. It was only for the movie intro and trailer. Because Sentinel was dead, and when Optimus and Ratchet take him to revive him, his eyes are not lit up. And he wasn't pretending to be dead. So how can his eye light up, and then later in the movie he's dead again, and they revive him? Yeah, doesn't make sense.
Reign of Starscream, the first movie prequel comic. The line "Wanna Bet?" was used in the fifth issue of the comic when Starscream killed Dreadwing for his betrayal on Cybertron. Dreadwing even went to use the line "I still function".
It could also be that in that deactivated mode, there is still some mechanical functionality inside the robot, such as the inner workings of the braincase behind the eye.