Here are the steps that has to be followed in-order to reset pram on Mac.
The first step require you to shut down the computer.
Now you can locate the keys on the keyboard: Command, Option, P, and R. Here, you are require to hold these keys down simultaneously in step 4.
Now you can turn on the computer
Instantly press and hold the Command-Option-P-R keys. Be quick to tap this key combination before the gray screen appears.
You an can continue holding the keys down until the computer restarts, and you hear the startup sound for the second time.
Release the keys.
Resetting PRAM may change some system settings and preferences. Use System Preferences to restore your settings.
Are the tiny amount of your computer’s memory, called “parameter random-access memory” or PRAM, stores certain settings in a location that Mac OS X can access quickly.