Troubleshooting a Mac Computer That Won't Recognize Internal Hard Drive

Before you blame your hard drive, check to make sure your monitor works correctly. You could have a problem with your monitor if the monitor doesn't light up with the gray boot screen. A broken monitor won't affect any of the other functions, such as fan noise, the startup chime and the backlit keyboard on supported MacBooks. If your computer exhibits any of these symptoms, you could need to replace the monitor or in extreme cases, the entire logic board.

When you press the power button on your Mac, check to make sure you don't have a power issue. Check that the light on your MagSafe adapter is showing green. If you're using a MacBook, push the round battery indicator button on the left side of the computer. A string of green dots should appear if you have a normally functioning battery. If your computer makes no sounds whatsoever when you try to start the computer, then you have an issue unrelated to the hard drive. A Mac still attempts to boot and reaches the gray screen even if the computer doesn't have a hard drive installed. Check to make sure your power outlet works by plugging in a lamp or other electronic device. Sometimes, you may only need to buy a new power adapter to fix the problem.

Unplug all devices not essential to the functioning of your computer. This includes speakers, printers and any unnecessary USB devices. You computer may appear to not recognize your hard drive due to a faulty USB connection. Sometimes your USB devices malfunction and draw too much power from the computer. When a device draws too much power, the computer shuts itself down or disables the port drawing the excess power to prevent a surge that could damage your computer.

The System Management Controller guides many low-level settings on your Mac. These settings could cause problems with power and boot procedures and may exhibit symptoms that mimic a hard drive problem. Try resetting the SMC to make sure that your problem isn't related to one of the many settings that the SMC handles.

On desktop Macs you can reset the SMC by shutting down the computer, unplugging the power adapter and waiting 15 seconds before plugging in and powering on the computer.

On a MacBook with a removable battery, shut down the computer, unplug it, remove the battery and hold the power button down for five seconds. Release the power button, replace the battery, plug the computer back in and turn the computer on to see if the issue is resolved.

On portables with batteries you can't remove, shut down the computer and plug in the MagSafe adapter. Press and release the "Shift-Control-Option" keys along with the power button simultaneously, release and then start your computer.

Sometimes your Mac may lose track of the location of the startup disk. This can happen when you force your computer to shut down using the power button, or when a newly installed application wreaks havoc with your system. You can manually select the startup disk by holding down the "Option" key while the computer boots. To check the disk for errors, click on the hard disk labeled "OS X Recovery" and select the "Disk Utility" option. Once inside the Disk Utility, click the "First Aid" tab, select your disk and then click the "Repair" button.

If your operating system is badly corrupted, reinstalling it may be the only option. If Disk Utility advises you of a failing hard disk, you should immediately back up as much data as possible and install a new hard drive if possible. Otherwise, you can hold down the "C" key while the computer starts and select the option to "Reinstall OS X" and follow the prompts to reinstall your operating system. The process of reinstalling your operating system deletes everything, so make sure you back up as much data as you can.

Information in this article applies to OS X Mountain Lion. It may vary slightly or significantly with other versions or products.