First, I sure would like to know about this update. What kind? From where? The info is essential to determine if it's a Trojan Horse.
Is it possible for you to boot in safe mode with networking? (taping F8 during boot time?)
If not, from the black screen, do you have access to command prompt or to your task manager (alt+ctrl+del)?
I am awaiting your reply before any other help can be provided.