How to Mount your iPod in Disk Mode
The secrets of Disc Mode
You've tried to get the iPod to connect to your computer and the computer just doesn't recognize the device. Getting the iPod to show up in your computer's storage or in iTunes is called "mounting." We say it doesn't mount if the computer doesn't notice that the iPod is connected. The most direct route to forcing the computer to see the iPod is to put the iPod into disk mode.
Before we go into disk mode lets consider a few preliminaries.
High Power USB 2.0
First, make sure the iPod is plugged into your computers high powered USB port that uses USB 2.0. Almost any computer made after 2001 will have one. If your iPod isn't mounting you should first ensure it's securely connected via USB, and if it is, you can try another USB port. If the USB port is part of a USB hub, try connecting the iPod directly to the USB port on the computer. This will ensure the iPod is getting all the power it can from the USB port.
FireWire
Older iPods, including the iPod 4th gen, use FireWire, which almost always has enough power for the iPod. However, you may lack the power to run the iPod if you're using a FireWire chain of devices. Ensure the iPod is directly connected to the FireWire port on the computer and not part of a FireWire hub or chain.
iPod Reset
The first step in the iPod reset is to slide the hold switch across to hold and then back again to lock / unlock the iPod. This is helpful to first ensure your problem isn't simply that the iPod is locked, as well as to force it unlocked if the switch appears in the unlocked position but is really locked. It's possible the switch mechanism inside the iPod may make it appear to be unlocked when really it is locked. Go on to perform an iPod reset after you've completed the hold switch.
To perform a reset, first identify which iPod you own. The reset method depends on the iPod's generation and type.
Reset first generation to third generation iPods: Press and hold the following combination of buttons for 10 seconds: Menu and Play / Pause.
Reset fourth generation iPod's including iPods Photo, Nano, Video and Mini: Press and hold the following combination of buttons for 10 seconds: Menu and Select (Select is the center button)
When you have performed the reset, you'll see an Apple logo. Let go of the button combination that performed the reset. Now hold down the Fast Forward and Rewind buttons at the same time. This forces your iPod into disk mode. If the iPod fails to mount restart the computer.
Now that it's in disk mode, the iPod should say "Disk Mode" at the top of the screen and "OK to disconnect" near the bottom. The computer should now read the iPod. If it doesn't, try another USB or FireWire port.
To get the iPod out of disk mode reset the iPod again.