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Hello. The progress bar will only appear for firmware updates (which this is not).. or during a "safe mode" boot (which requires holding the SHIFT key at start up)... or your Mac is trying to diagnose an issue with the boot volume.If you're getting a start up chime and an apple logo, that means your Mac has passed something called POST. Post means your Mac has passed a basic hardware check, and is now looking for the start up volume, typically your internal hard drive.If this progress bar shows up every time you boot your Mac, it's trying to self-diagnose an issue with the start up volume. Your next best step is to boot from your Recovery CD (Snow Leopard or earlier) or from the Recovery Partition (Lion or Mountain Lion) and run Disk Utility to check your start up volume.
If your Mac is running Lion or Mountain Lion, you can boot from the Recovery Partition by holding "Command" + "R" at start up. This will present you with a set of tools, one which will be Disk Utility.If your Mac is Snow Leopard or earlier, insert your Recovery DVD, restart and press "C". This will boot from the recovery disc. When it's finished booting, choose Disk Utility from the menu bar.
I tried starting from the OSX recovery disc, holding the "C" key and it began to beep three times (pattern)