Mac OS X v10.6: Gray progress bar appears under Apple logo during startup
A gray progress bar may appear below the Apple logo each time the computer starts up. The bar may remain a few minutes before the Finder or login window appear. Learn what to do if this happens each time you start up the computer.
If this happens each time your Mac starts up, it probably indicates Mac OS X v10.6 is attempting to diagnose and resolve an issue with your hard disk or the data on it.
Important: If this occurs each time you start your Mac, you should back up your important data because hard drive issues can potentially lead to data loss, You can use Time Machine to back up your system to a different disk, or back up important files to MobileMe, a burnable disc, or a different location if available. See How to back up and restore your files and Alternatives for backing up your computer for more information.
Start up from your Mac OS X v10.6 Install disc and use Disk Utility to try to repair any disk issues. See the "Try Disk Utility" section of this article for instructions.
In the event that Disk Utility finds issues it cannot repair, and you have a backup as mentioned above, you may need to erase the hard drive. After erasing and reinstalling Mac OS X v10.6, restore your Time Machine backup or important files you backed up.
You may notice the gray progress bar resembles a Safe Mode startup, or an EFI firmware installation or restoration; however this issue is not related to firmware.