Once your iPod is connected to the primary computer you will open iTunes. Once you disconnect your iPod from your computer it shouldn't be locked anymore. If this doesn't work then try to restore your iPod to the factory settings. However, keep in mind that this will delete all data. You can find more information here: http://www.everymac.com/systems/apple/consumer_electronics/ipod_faq/ipod-reset-code-to-unlock-screen.html
