on the keyboard, with one hand, hold down the Command, Option (Alt), P and R keys, then press the Power button to start your Mac up.with the Mac still shut down, connect your USB mouse and keyboard.Once that is connected and fully home, release the Power button hold the Power button in (pressed) while you reconnect the mains power cable (and no other cables).remove all connecting cables, including the mains power cable, and leave it for 15 seconds or longer.shut your Mac down, if necessary forcing shutdown using the Power button.You need to follow this sequence carefully: Together, these are the modern equivalent of ‘zapping the PRAM’ on old Macs, and more. If you still cannot start it up despite it passing hardware tests, the next step is to try resetting its SMC and NVRAM. Your Mac may be less convinced that it should be working normally. If they too are normal, you should be fairly confident that nothing significant is wrong with your Mac’s hardware. If no fault is found, you can run the Extended diagnostic tests: these normally take an hour or so, and test memory thoroughly, for example. If a fault is found, you will be given a description which an Apple technician can use to identify the repair necessary. These hardware diagnostics will first establish your Mac’s model and hardware details, which you can view in their last tab, and then invite you to press the T key to run the basic tests. You might be able to get these to run locally by holding the D key down during startup, but they are more likely to run properly when remote, using Opt-D instead. One good way to test this is to run the remote Apple Hardware Test (older Intel Macs) or Apple Diagnostics. If you are still not able to start your Mac up, this is probably the right time to ask whether this is a hardware or software issue. You can select the drive by holding the Option key during startup, or force it using the C key (on a good day). These are ideal when Internet connection speeds are not superfast, or where you are running several Macs. If you cannot do so using that locally, and you have a fast broadband connection, remote Recovery mode (Opt-Command-R) will download a barebones version of OS X and its tools for you to try to check and repair the hard disk.Ī bootable OS X install disk – typically a USB memory stick, or hard drive – can be used for recovery and to re-install OS X, if you have one prepared.
A good way to check that is to start in (local) Recovery mode (Command-R held during startup), and from that run Disk Utility. If it does not, the next question is whether this is a hard disk problem. Sometimes removing other peripherals will allow your Mac to start up normally again. Then disconnect all peripherals except for your network connection, any display cable, and a mouse and keyboard (preferably wired USB models not Bluetooth wireless). If your Mac will not restart in either normal or Safe mode, or gets so far before freezing or restarting again, you should shut it down again, if necessary forcing that by holding the Power button again. If either of those gets it up and running again, you can inspect the logs and try to work out if there is any remaining issue which needs to be sorted out: other articles listed below explain how to do that. Normally your next step will be to try to start it up again or, if that does not work or you suspect a more significant problem, to try starting it up in Safe mode (Shift key held during startup). If frozen, you forced it to shut down by holding the Power button until it shut down – never by just pulling the power cable or turning the mains supply off, please. Maybe, like me, your Mac suffered the dreaded ‘blue screen of death’ (BSOD), or just froze, or will not start up (or restart) properly.
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