Hi,
First, try a Safe Mode boot. That deletes system caches that can help after an update.
To start up in safe mode:
- Start or restart your Mac, then immediately press and hold the Shift key. The white Apple logo appears on your display. If you don't see the Apple logo, learn what to do.
- Release the shift key when you see the login window. If your startup disk is encrypted with FileVault, you might be asked to log in twice: once to unlock the startup disk, and again to log in to the Finder.
To leave safe mode, restart your Mac without pressing any keys during startup.
If that doesn't help, check the startup disk to see if it needs repairing using OS X Recovery.
Startup up your Mac while holding down the Command + R keys.
From there you should be able to access the built in utilities to verify and repair the disk if necessary and restore OS X using OS X Recovery.
* message edited by CS