What to do if your iMac won't start

Q I have a relatively new iMac that has suddenly stopped working. There is the Mac sound when it starts but the screen stays white. I have tried unplugging everything but the keyboard and mouse and that hasn’t helped. I use Mac OS 10.

Nathan Peters

A We have seen problems like this that have been relatively simple to fix, as long as you know the correct keys to use. First try a Safe Boot by holding down the Shift key as the Mac starts. This will take much longer than a normal boot. Try restarting as normal if that works.

If that doesn’t work you may need to reset some of the Mac settings to do this. Again this is not too difficult. Make sure the Mac is completely shut down, you may need to hold down the power key for several seconds.

Get ready to hold down the following keys altogether: Command, Option, P and R. Turn on the Mac and press these four keys before the grey screen appears.

Keep the keys held down until the Mac starts again and you hear the start-up sound a second time. For more information see the Mac help pages.

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