Okay, seems like a pretty common problem. Try this:
* Hold Option (Alt) + Command + R while starting up. This will start the Mac using Internet Recovery.
* Hold Option + D while starting up. This will start Apple Diagnostics using the internet (versus using offline mode).
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* Create a macOS USB OS installer using another Mac. [guide|66371]
+
* Create a OS installer USB thumb drive using another Mac. [https://support.apple.com/en-us/101578 https://support.apple.com/en-us/101578|Create a bootable installer for macOS]
Okay, seems like a pretty common problem. Try this:
* Hold Option (Alt) + Command + R while starting up. This will start the Mac using Internet Recovery.
* Hold Option + D while starting up. This will start Apple Diagnostics using the internet (versus using offline mode).
* Create a macOS USB partition using another Mac. [guide|66371]
Hope this helps