Questions and Answers
Installer Error - This copy of the Install OS X El Capitan application can’t be verified. It may have been corrupted or tampered with during download
The installer is not corrupt , the message you are receiving is due to a certificate signing issue that Apple has implemented ( Feb 2016) for the install of OS X. The date on your system is too old or too new. To get by this false message, Use Terminal to change the date.
When you get to the install OS X screen , use the top menu , utilities and choose Terminal.
At the prompt enter this exactly sudo date 0101120116
press Return, and enter your password.
Quit Terminal and continue the install.
Holding option key does not work , does not show Startup Manager?
First you should be using or need to use a mac keyboard.
Not all PC keyboards are recognized at startup to engage the key combination.
On some keyboards only the Option Key on the left side will work.
Some older Mac's need a "wired" keyboard as the bluetooth seems to lag and does not register in time .
If your still having problems , reset the SMC and PRAM and try again as your having a hardware problem.
How do I reset NVRAM or PRAM?
Shut down your Mac, then turn it on and immediately hold down these four keys together: Option, Command, P, and R. Keep holding the keys during which your Mac might appear to restart. You can release the keys after the second startup sound.
How do I reset the SMC (System Management Controller)
Mac desktop computers ( iMac , Mac mini , Mac Pro )
1. Shut down your Mac. Unplug the power cord.
2. Wait 15 seconds.
3. Plug the power cord back in.
4. Wait five seconds, then press the power button to turn on your Mac.
Mac notebook computers
If the battery is nonremovable:
Shut down your Mac and unplug the MagSafe or USB-C power adapter from your computer.
Using the built-in keyboard, press Shift-Control-Option on the left side of the keyboard, then press the power button at the same time. Hold these keys and the power button for 10 seconds.
If you have a 2016 MacBook Pro with Touch ID, the Touch ID button is also the power button.
Release all keys.
Reconnect the power adapter.
Press the power button again to turn on your Mac.
If the battery is removable:
Shut down your Mac and disconnect the MagSafe power adapter from your computer.
Remove the battery.
Press and hold the power button for 5 seconds.
Reconnect the battery and MagSafe power adapter.
Press the power button to turn on your Mac.