Template:IPodReset4G

From Mac Guides

As with all clickwheel iPods, you can reset this iPod by first toggling the hold switch on and off and then simultaneously pressing the select (center) and menu buttons for approximately 5-10 seconds. This is a common fix should your iPod behave unexpectedly or lock up. Once reset, the iPod should display an Apple logo for a few seconds before showing the main menu. This procedure is similar to rebooting a computer and damages none of your music or data.