To start off you must first determine whether or not your hard drive is really crashed or not. If you can not boot to your Apple computer is the first stop for the diagnosis should discussions.apple.com. Does the gray screen, the error message or see strange flicker? Regardless of the specific symptoms you are experiencing, the first place to check out the Apple discussion page to see whether other users have experienced similar problems. Often there are posts from other Apple owners who can detail a simple decision based on what is happening.
Tips: Be sure to select the appropriate categories (Apple desktop, PowerBook, etc.) and its model, so you're sure to get accurate search results. Also, try several different variations of the keyword in the search, because people often describe things differently.
Next we want to find out if your drive will boot at all. If you have a Macintosh around, and then turn off the computer in question and turn it into a working Mac with a FireWire cable. Now you can turn on the drive in question, hold down the T as the Mac tries to boot. If successful you'll see (possibly) damaged disk on the desktop of another computer. A good time to make a backup of important files!
Advice: After backing up critical files, it is best to return to talks page again and do more searches, because chances are very high that they do not have a damaged disc, but that something has become corrupted. Once in a while, boot up the drive with a different Mac will actually solve the problem so make sure you try to boot up the machine again. (Do not forget to pull the drive garbage off the computer and unplug the cables !)
If none of the above works, then the best thing to do is take some of the following Macintosh data recovery software and see if the filesystem is just corrupt, or if there really is a bigger problem. Follow the links below for more details on what software to get.
The process is simple -. You can download some free software, do a test to see if the data is recoverable, then buy the software if you want to take the next step is to back up all your files
If the data recovery software does not work, then your next step will be to send the drive off specialist, because at this point, you've probably got a mechanical problem that can not be fixed with any off the shelf solutions. Best of luck!