More fixes for this surprisingly problematic update.
Zapping PRAM/NVRAM has only a few uses and this is one of them.
Margin Note: Why are three chimes recommended for a PRAM/NVRAM reset?
Troubleshooting Mac OS X 10.2.4: Resetting NVRAM for sleep problems
The PRAM The Parameter RAM is a small amount of "nonvolatile" RAM (NVRAM) that holds various settings that the system can use before the operating system loads, and maintains these settings even when the computer is turned off. There is a small battery
Many articles you read on Mac troubleshooting mention troubleshooting methods like resetting the NVRAM, starting in FireWire Target Disk Mode, starting in Safe Mode, or starting in Single-User Mode, but fail to explain exactly how to do that.
The OS X boot arguments are useful for troubleshooting problems with system startup and how the system behaves when running.
If you have a Bluetooth keyboard, OS X may ignore keystrokes at startup for booting into Safe mode and other optional boot environments.
A quick PRAM reset or settings change may help a stubborn MacBook that refuses to enter clamshell mode.
Often when troubleshooting problems in OS X, booting to Safe Mode is one step to minimize the boot environment. Here are some options for how to do this.