Summarize the following:
This is one of the more difficult repairs to attempt yourself, so make sure that you can't fix the issue using one of the other methods in this article first. If you've tried everything, you can try replacing your hard drive as a last-ditch effort.   If you iPod is making a clicking sound and the "sad iPod" image appears on your screen, then the hard drive most likely needs to be replaced. Replacement hard drives can be ordered online, or you can scavenge a drive out of another iPod that is the same model. All versions of the iPod Touch, iPod Shuffle, and iPod Nano use flash memory instead of a traditional hard drive. This means there are no moving parts that can fail or connections that can become severed. There is no practical way to secure or replace an iPod Touch hard drive, as the flash memory unit is built into the circuitry. Make sure that the iPod is turned off and locked with the Hold switch toggled on before opening your iPod. This will ensure that you don't accidentally turn it on while working on it. Follow the steps in the previous method to remove the back from your iPod to expose the hard drive. Lift the hard drive from the top of the iPod. Don't try to pull it out completely. Remove the rubber bumpers and shock absorber and set them to the side. You will see a cable at the bottom the drive that attaches the drive to the circuitry. Gently work the cable out of the drive, using either your fingers or a screwdriver. Once the cable has been detached, you should be able to completely remove the drive from the housing. Once you have pulled the drive out, take off the foam cover and put it on your replacement drive. Put the rubber shock absorbers on it as well. Insert the new drive in the same direction that the old drive was installed. Gently insert the cable so that the hard drive can send and receive data from the iPod's motherboard. Close up the iPod and ensure that all of the tabs click. With the new hard drive installed, all that is left is to perform a restore on the iPod. See the first method in this article for detailed instructions on restoring the device.

Summary:
Ensure that there are no other options. Toggle the Hold switch on. Open your iPod. Lift up the hard drive. Pull the drive out slightly. Remove the drive. Install the new drive. Restore the iPod.