Connect the iPod to the cable that you use to transfer music from your PC. Connect the cable to your PC as well and this should automatically launch iTunes if you have it installed. If not, make sure to install the free program, because it's the only supported software for managing your iPod music. If it does not launch automatically when your iPod is plugged in, launch the iTunes software manually.
Cancel synchronization right away as it will erase the music files on your iPod. Click on the name of your iPod in the Devices section of the left panel. This will take you to a screen that contains the general information about your iPod, such as size, name and available options. Select the checkbox that allows you to manually manage music, as that will keep your iPod from attempting to sync again and potentially erase your music.
Check the option at the bottom called "Enable Disk Use." This will allow you to browse your iPod as if it is a hard drive or jump drive attached to your computer. Now eject your iPod so these settings will take effect next time you connect your iPod to your PC.
Change the folder options on your PC to be able to view hidden files and folders. Double-click your "My Computer" folder and go to the Tools menu at the top. Select "Folder Options" and go to the View tab along the top. Check the "Show Hidden Files or Folders" checkbox and then click "Apply."
Reconnect your iPod. In your My Computer folder there will be a removable storage device that was not there before. This is your iPod, and you can now browse it like a hard drive. Navigate to the folder named "iPod_Control" and inside of it will be a folder called Music. This is where your music is stored on your iPod. Copy this folder back to wherever you want on your PC and you are done.