Power button stuck?

Take it to the apple store but in the meanwhile, Go to settings app > General > Accessibility > Assistive touch > Switch ON > Tap the white circle in the grey square > Click Device > Click Lock Screen. That is how you can turn it off. If you do not like Assistive Touch, then you can just wait for it to turn off by itself. It wastes battery but to help go to Settings app > General > Auto-Lock > 1 minute. Now it will automatically switch to lock screen faster. Obviously to turn on the device click the home button. Has it been one year since you bought the iPod? If it hasn't all iPods are under a one year warranty. I hope this helps you. -Pandaluver2334

The iPod Nano doesn't have Assistive Touch.