OS X Mavericks: If you see a gray screen at startup
If you see a blank gray screen after starting up your Mac, you may have a problem with a firmware update. If you see a gray screen with an Apple logo (with or without a gear icon) and a flashing question mark, you may have a problem with missing, incompatible, or damaged software.
- Make sure the latest firmware for your Mac is installed. Check the Apple Downloads website for the latest versions. If you recently installed a new version of your computer’s firmware, try installing it again.
- If you have just installed OS X v10.8, make sure your Mac has at least 1 GB of memory and 9 GB of available disk space. If you are unsure of your computer’s specifications, refer to the printed instructions that came with your Mac.
If your Mac doesn’t meet these specifications, reinstall your previous version of OS X.
- If you are starting up from a DVD, it must be a disc that came with your Mac or OS X retail package. Discs from other Mac models may not work with your Mac.
- Repair your startup disk or disk permissions using Disk Utility.