The iPod model A1236 is the iPod 3rd generation Nano. This specific model Nano is characterised by its small, square shape; the models before and the models after are long and narrow. If you find that some files will not open on the iPod or you continuously receive errors, you have two different options of trying to correct this issue. You can reset, or restart, the iPod, or you can reset the iPod to its factory default settings. You will lose all of your information if you choose to restore the device to its factory settings.
Open iTunes on your computer and connect your iPod to the computer using the iPod USB cable. Connect the small side of the cable to an open USB port on your computer, and connect the large side to the bottom of your iPod.
Select the Nano device on the left side of the window.
Click the "Restore" button within the devices "Summary" tab and confirm that you want to restore the iPod to its factory settings. The restoration process begins after you confirm.
Wait for the progress bar to complete. The restore will be finished when you see the “iTunes Setup Assistant” appear on your computer screen.
Slide the "Hold" switch to the on position, and then to the off position.
Press and hold the centre button and the "Menu" button at the same time.
Hold the buttons for six to eight seconds until the Apple logo appears. The iPod will reset after the logo appears.