ChitlinsCC provided you with a link to an article with additional information. Unfortunately, recent support documents appear to focus mainly on the latest operating system versions, which may be confusing for users of older Macs. The following excerpt from an earlier article (TS1440 - April 06, 2011) could possibly be of some extra help in this case:
1. Select your Mac OS X startup disk with Startup Manager by restarting and holding the Option key. After your Mac starts up, restart again to verify that the flashing question mark does not appear.
2. If the issue persists, insert your Mac OS X installation disc. Be sure to either use the disc that came with your Mac, or, if you installed a later Mac OS X version from disc, use the newer disc.
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3. Restart the computer, then hold the C key during startup.
4. From the Utilities menu, choose Disk Utility. Don't click Continue.
5. Select your Mac OS X disk (named "Macintosh HD" by default) in the left side of the Disk Utility window.
6. Click the First Aid tab.
7. Click Repair Disk to verify and repair any issues with your Mac OS X startup disk.
8. After repairing the disk, try to start up normally.
Important: If Disk Utility finds issues it cannot repair, you may need to back up as much of your data as possible (or use Time Machine to back up to a different disk), then erase the disk and reinstall Mac OS X. You should back up important files and data before erasing a drive. Erasing deletes everything on the hard disk (including things on your desktop). Also, you can install Mac OS X onto an external disk, start from the external disk, and use Migration Assistant to transfer items from your usual internal Mac OS X startup disk to the external disk, then erase the internal disk and reinstall Mac OS X.
9. If the issue persists, and Disk Utility didn't find any irreparable issues, quit Disk Utility, quit the Installer, select your disk when prompted, and restart.
10. If the issue continues, reset PRAM. Note: After resetting PRAM, if the computer starts up normally, reselect the startup disk in the Startup Disk preferences.
11. If none of these steps resolve the issue, start up from the Mac OS X Installation disc and reinstall Mac OS X.
