MacBook Pro not starting up at all

Having this problem too. If that's what's happening, how long did it take? Mine's been unresponsive for hours -- all day now. It's an oldish MBP (the last 17" model they made) and it worked fine but I haven't been using it for a while. I tried to fire it up to use the optical drive (wanted to load a CD onto my 13inch MBP), but nothing. Just as OP described. Green light on the power cord but no other sign of life --all maneuvers (reset SMC, etc) no effect. It's been plugged in all day like this. How many hours did your update take?

Try resetting the SMC

Reset the System Management Controller (SMC) on your Mac - Apple Support

You said "It's like dead not starting up."

Does that mean it shows no sign of life? Power light light?

Hear chime?

Hear fans?

If resetting the SMC does not work then make an appointment at the Genius Bar of an Apple store since it appears you have a hardware problem.

Apple Retail Store - Genius Bar

https://www.apple.com/retail/geniusbar/

Similar happened to me a couple weeks ago Big Panic. Thought power switch was broken.

It turned out that by coincidence an auto upgrade to El Capitain was underway.

Hope that is/was your situ