When you turn on your computer and get a grey or blue screen (or it gets stuck at the Apple logo) that never loads OS X, it’s a pretty good cause for concern. This can happen for a number of reasons, so it’s one of the most frustrating things that can happen to a Mac, and troubleshooting it is no easy task. So, let’s break it down into a few steps you can take to figure out what’s going on.
Step One: Disconnect All Peripherals
One of the main causes of a grey or blue screen on startup is incompatible hardware connected to the machine. This might be a printer, an external hard drive, or even a USB hub. So, disconnect everything except the mouse and keyboard, and restart your computer.
If your Mac starts this way, then it’s an issue with one of those peripherals. You have to trial-and-error your way through to figure out which one, so connect them back into your computer one by one, and restart. If one of them causes your computer to hang on the grey screen again, you’ve found your issue.
Step Two: Perform a Safe Boot
Safe boot makes your Mac boot up with the minimum amount of drivers needed to make it work, and it checks your hard disk in the process (it might take a bit longer to boot up). Do do this, start up your computer while holding down the Shift key until the Apple logo passes. If your Mac starts up with the safe boot, go ahead and restart the computer again and see if it boots up normally (as odd as it sounds this fixes the problem a surprising amount of the time). If not, it’s time to give the hard drive a closer look.
Step Three: Run Disk Utility
If you still can’t boot up OS X normally, it’s time to run Disk Utility and check out your hard drive:
- 1. Boot up your computer while holding down Command+R (if you’re running Snow Leopard or earlier, find your OS installation disc, put it in the drive, and reboot your computer holding down C). This will boot you into a diagnostic mode.
- Select the Disk Utility Option.
- Select your hard drive, and click “Verify.” Wait for Disk Utility to finish running.
- If problems pop up, click “Repair Disk.”
- If nothing pops up, click “Repair Permissions” and wait for Disk Utility to scan your hard drive again.
- If Disk Utility finds and repairs some problems, go ahead and reboot.
Note: In a lot of cases, running Disk Utility will catch problems with startup issues. Sometimes a single file with the wrong permissions can cause the whole system to collapse, or if something’s not in the right place it won’t boot. If this doesn’t work, you have a lot more problems to look into.