PRAM/NVAM Reset on Mac

NVRAM corruption is fairly uncommon, but if your Mac seems to take forever to figure out which disk to boot from, if it starts up with the wrong screen resolution, or if you have weird audio problems (like there’s no sound whatsoever, or the menu bar’s volume control is grayed out), it doesn’t hurt to reset the NVRAM—it’s quick and harmless. NVAM Resets have cleared up other strange anomalies on Macs as well so we recommend starting here if you have any odd issue going on with your Mac.

To reset your NVRAM, you use exactly the same procedure you once used to reset PRAM.

1. Shut down your Mac.
2. Press the power button, and as soon as you power up the laptop, hold down Command-Option-P-R.
3. Keep holding down those keys for about 20 seconds. Then let go and allow your Mac to continue starting normally. If you have an older Mac that chimes at boot, hold down the keys until you hear a second startup chime. 
4. Then check the Startup Disk, Display, and Date & Time panes of System Preferences to make sure they’re set the way you want them.

If you hold down Command-Option-P-R at startup and you see nothing but a gray screen that doesn’t change for several minutes—no Apple logo, no progress bar, no second startup chime—don’t panic. The most likely cause is that your Mac isn’t registering the key presses due to wonkiness with a USB device. Disconnect all USB devices (except your keyboard, if it’s a wired keyboard), hold the power button down until the Mac shuts off completely, and then press it again and immediately hold down Command-Option-P-R.

If that doesn’t work and you’re using an external Bluetooth keyboard, try plugging in a USB keyboard instead. If you’re able to reset the NVRAM successfully with the wired keyboard, you can disconnect it and go back to your normal Bluetooth keyboard.