Official Apple Support

Details of official Apple support for each product can be found here:

• iPod Classic
• iPod Touch
• iPod nano
• iPod shuffle
• iPhone

iPod Troubleshooting Guide

The 5 Rs

Apple advocate 5 basic steps for resolving iPod issues:

• Reset
• Retry
• Restart
• Reinstall
• Restore

You can find specific instructions for your particular model here:
iPod 5Rs Troubleshooting Assistant