Your MacBook Pro (A1151) needs to be activated by pressing the Alt key.
Your MacBook Pro (A1151) needs to be activated by pressing the Alt key.
Your MacBook Pro needs a manual boot sequence—pressing Alt and navigating to the selection menu is required. If it still won’t boot, there might be an issue with the boot device or system settings. Consider checking the power source, cable connections, and ensuring the macOS is properly installed.
It's a laptop I purchased on eBay, but the seller didn't understand why, and now I'm wondering the same thing.
Did you purchase a functional device or is it still untested? If it's the former, send it back and file a claim on eBay. If it's the latter, reset SMC and PRAM, boot into recovery mode if available, and perform a drive repair. If those steps fail, attempt a clean installation using an installer USB, wipe the drive with disk utility, reformat it as APFS, and reinstall macOS.