Hi there Panchinho!
I have a website here that can help you resolve this issue with your iPod classic. This website is the starting point for the iPod troubleshooting assistants, and can be found here:
You will want to choose the iPod model and generation that you are trying to troubleshoot, and then the assistant will walk you through some steps to attempt to resolve the issue. Take care, and thanks for visiting the Apple Support Communities.