-Shut down the computer.
-Locate the following keys on the keyboard: Command, Option, P, and R. You will need to hold these keys down simultaneously in step 4.
-Turn on the computer.
-Press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears.
-Hold the keys down until the computer restarts and you hear the startup sound for the 2nd time.
-Release the keys and let your system boot up.
Shut down your Mac. Next, power your Mac back on. Just after you hear the startup tone, press and hold the “Shift” key. You can release the Shift key after you see the gray Apple and progress indicator. Your Mac should boot up into Safe Mode. Then reboot your Mac and test under a normal boot up.
The best way is to boot for your original installation disk, and use disk utilities to "repair disk". If, for some reason, your installation disk isn't handy you can do the same thing by booting into single-user mode (by depressing the command (Apple key) and S keys at startup), which takes you to a terminal-like screen. At the prompt there, type the command: "fsck -yf" (without quotes and note the space). If it doesn't find the command, type /sbin/fsck -yf instead. If it complains about permissions type: "sudo /sbin/fsck -yf" and provide the admin password XXXXX prompted. If it finds errors, repeat this command until no errors are reported and you see the "...OK" statement. This check may need to be run up to four times on a system with serious problems. When you get the "...OK" message, type “Reboot”. Your Mac will restart and return you to the User GUI interface.
Reset the SMC of a MacBook or MacBook Pro’s with detachable batteries:
* Shutdown the MacBook/Pro and remove the battery * Disconnect the power adapter, hold the Power Key for 10 seconds * Release the power key and reconnect your battery and power adapter * Turn your Mac on * Let boot as usual.
Reset SMC of a MacBook or MacBook Pro’s with an internal battery:
Common symptoms of a dying hard drive
Hard drive is making a clicking, whirring, grinding, ping pong ball noise or any other type of unusual noises.
Hard drive is not spinning.
Computer is not recognizing the hard drive.
Sluggish loading of applications.
System freezes and hangs.
An interesting site - Hard Drive Sounds by drive manufacturer.