Thawing some deep freezes: Zapping PRAM/NVRAM
Zapping PRAM/NVRAM has only a few uses and this is one of them.
[Published Tuesday, July 17th]
Zapping a Mac's PRAM/NVRAM has, in the minds of some users, come to be thought of as a useless ritual -- a troubleshooting step that doesn't accomplish anything but is still recommended as a feel-good move when no specific solution presents itself. On the contrary, there are some issues where clearing the contents of PRAM and NVRAM can prove highly effective; in particular, problems with USB/FireWire device or RAM recognition, power management (including battery) problems and more.
We've now received reports indicating that zapping PRAM/NVRAM can resolve an issue where the system exhibits a "deep" freeze. This is a situation where the cursor stops moving, the clock stops moving, and no other system events will trigger response. We're not sure exactly why the procedure is effective in this case, but it could be a power delivery issue that occurs when processes are switched.
In order to reset PRAM/NVRAM, shut down your Mac, then start it back up while immediately holding the following keys: Command, Option, P and R. Hold the keys down until the computer restarts and you hear the startup sound for the third time.