Maybe, like me, your Mac suffered the dreaded ‘blue screen of death’ (BSOD), or just froze, or will not start up (or restart) properly. 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.

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 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.

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. Then disconnect all peripherals except for your network connection, any display cable, and a mouse and keyboard (preferably wired USB models not Bluetooth wireless).

Sometimes removing other peripherals will allow your Mac to start up normally again. If it does not, the next question is whether this is a hard disk problem. 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 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.

A 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. These are ideal when Internet connection speeds are not superfast, or where you are running several Macs. You can select the drive by holding the Option key during startup, or force it using the C key (on a good day).

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. One good way to test this is to run the remote Apple Hardware Test (older Intel Macs) or Apple Diagnostics. 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.

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. If a fault is found, you will be given a description which an Apple technician can use to identify the repair necessary. 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 they too are normal, you should be fairly confident that nothing significant is wrong with your Mac’s hardware.

Your Mac may be less convinced that it should be working normally. If you still cannot start it up despite it passing hardware tests, the next step is to try resetting its SMC and NVRAM. Together, these are the modern equivalent of ‘zapping the PRAM’ on old Macs, and more. You need to follow this sequence carefully:

1. shut your Mac down, if necessary forcing shutdown using the Power button;
2. remove all connecting cables, including the mains power cable, and leave it for 15 seconds or longer;
3. hold the Power button in (pressed) while you reconnect the mains power cable (and no other cables). Once that is connected and fully home, release the Power button;
4. with the Mac still shut down, connect your USB mouse and keyboard;
5. 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;
6. keep those keys held until your Mac restarts twice, with a second startup chime, then release them.

Following a significant BSOD event and that reset, your Mac may then take a long time to start up. It will initially run with its fans running full on: do not be alarmed, this is normal behaviour. Macs are designed so that, by default, they run with fans on full. It is only when everything is back to normal that your Mac’s SMC will be able to take charge again and set the fans back down to normal.

If at the end of all that, you cannot identify a hardware fault, and you still cannot get your Mac up and running again, it is time to book an appointment at your nearest Genius Bar, or with a qualified Mac technician, for them to run a full diagnostic check. I wish you fair winds, and success.

Useful items to keep in readiness:

• a cabled USB keyboard and mouse, which are not reliant on Bluetooth working properly;
• a bootable install USB memory stick for the latest major version of OS X, currently El Capitan (see below);
• a second Mac or iOS device with which you can browse Apple’s help info and other sources of help, including this blog;
• a good book; if you have a slower Internet connection or a large hard drive, these procedures can take a very long time.

To prepare a bootable USB memory stick, you will need to download the El Capitan (or appropriate) installer from the Mac App Store. Then download DiskMaker X (donationware). Using Disk Utility, initialise an 8 GB or larger USB memory stick to Mac extended (HFS+) format. Ensure the OS X installer is in your Applications folder, then run DiskMaker X to set up the USB memory stick. It will take a long time to copy the files to the stick, but will inform you once it is done.

Useful links:
This blog –
My Mac don’t work – troubleshooting tools and techniques
Generic troubleshooting: how to fix something that doesn’t work
Restoring firmware after interrupted firmware update
The Eclectic Light flickers: my iMac might be dead
Service with a Smile – advanced troubleshooting of services and the startup process
Thanks for the Memory
Crash crash – Crash Reporter and ReportCrash, the crash handlers
Recovering from a hard crash – when your startup drive is missing or damaged
Cause of Death – how disks become corrupted and crash
Q&A – Dead Mac recovery – recovering files from a dead Mac
Log race – understanding and using Console’s logs
Obscured by clouds: how to lose your audiobooks – info on restoring previous purchases from the iTunes Store
Magsafe compatibility – which power supplies can be used with which laptops?

Apple –
Startup key combinations
Apple Hardware Test
Apple Diagnostics
Recovery mode
Safe mode