Summarize this article in one sentence.
Restoring the iPod may require downloading the newest version of iTunes or the latest iPod software. Check to make sure you have the latest version by clicking on the iTunes menu, and selecting Check for updates... After a few moments, it should be listed in the left frame of the iTunes window. If you don’t have the frame open, you can select your device from the dropdown menu in the top-right corner of iTunes.  Click on your iPod to open the Summary tab of the main iTunes window. If your device is not recognized and the display shows a sad face, try putting the iPod into Disk Mode before restoring. If you cannot enter Disk Mode, then there is a hardware issue. This will erase everything on your iPod and restore it to factory conditions. Accept the warning prompts and your restore will begin.  Mac users will be asked for the administrator password. If using Windows, you may see one or more restore options prompting iTunes to automatically download the latest iPod Software. Holding down the SHIFT key before clicking the Restore button will allow you to browse your computer for version of firmware you wish to use. iTunes will display a progress bar while it is working. When this stage is done, iTunes will present one of two messages with instructions specific to the iPod model you are restoring:  Disconnect iPod and connect it to iPod Power Adapter (for older iPod models). Leave iPod connected to computer to complete restore (applies to new iPod models). During the second stage of the restore process, the iPod will display a progress bar on the screen. It is very important that the iPod remain connected to the computer or iPod power adapter during this stage. The progress bar may be difficult to see because the backlight on the iPod display may be turned off. Once the restore process is complete, iTunes will open the Setup Assistant. You will be asked to name the iPod and select your sync options. At this point, the iPod has been fully reset. Sync it to your computer to reload your music.

Summary:
Make sure that your computer has an active internet connection. Launch iTunes. Connect your iPod to your computer. Click Restore. Wait for the first stage of the restore process to complete. Keep the iPod connected. Setup your iPod.