Mac starts up, but the screen is garbled

With a 15-inch MacBook Pro (2011-2013), graphics processor failure is a known problem. Apple may repair later models (see bit.ly/ mbpvidiss) but otherwise workarounds (such as bit. ly/gpuwkrnd) are poor/impractical. For other models, try Apple Diagnostics (see page 23). If your Mac starts up with a flashing question mark icon, it means it can’t find a drive with a macOS installation. Let it try; if it does eventually start up, go to System Preferences > Startup Disk and select the correct drive. If not, try macOS Recovery (see page 23). If your Mac starts up with the screen overlaid with ugly text, it’s a kernel panic. Restarting again may work. If not, restart in safe mode (see page 22) and install any software updates. No? Unplug all peripherals, restarting them one at a time. If the screen stays gray, be patient as macOS may be doing housekeeping. Still nothing? Try safe mode with peripherals disconnected, as above. Reset the SMC. No? If possible, remove any extra memory you’ve added (with power disconnected) and try without it. >>> An app is playing up If an app behaves oddly, quit (or force quit — see page 19) and reopen it, restart your Mac, and check for updates (in the Mac App Store or from the app’s menus). No joy? The app’s preferences may be corrupted. Quit the app, switch to Finder and go to ~/Library/ Preferences (see ‘Where’s my Library folder?’, page 20) and drag anything obviously named after that app to the Trash. With luck the app will now work, but you may have to set its options to your liking.

>>> An app crashes while running If an app you’re using, or have left open, stops working or behaves oddly, save your work if possible, ideally as a new file (File > Save As) in case the version in memory has become corrupted. Then quit the app (Cmd+Q), or if that doesn’t work, force it to quit (see right). >>> An app refuses to run If an app’s icon shows a no–entry sign, it’s incompatible with your version of macOS. Check with the app’s maker for a new version. If an alert warns that an app is ‘not optimised’, it’s 32–bit and will need a 64–bit update, for now, however, you can still use it. If an alert says the app ‘can’t be opened’, see page 26 for the solution.