iPod 4th Gen No Boot

I think that hard drive is bad.

Some extra info: I have a 4th gen iPod (monochrome screen). I replaced its hard drive with a 64GB compact flash card on an adapter. I bought the adapter many years ago, but it looks like one of these on Amazon

http://www.amazon.com/CF-Pin-1-8-IDE-Adapter/dp/B004FCY7WQ

and I also see similar items on eBay. I can't tell if this is exactly the one I have. It's NOT the type with the "ZIF" connector; those are for 5th gen and later iPods. The only minor complication was for the jumper used to set it as master/slave. It sticks up too far. I just bent the two metal "pins" (where you place the jumper to set as master) by 90º using needle-nose pliers. That design flaw may have been corrected by now.

SD ("SDXC") cards at the same capacity are usually cheaper than Compact Flash. You can put an SD card in an SD-to-CF adapter, and then put that combo in the iPod-CF adapter. It needs to be the thinner "Type I" adapter. "Type II" is thicker, and may not fit in the iPod's casing. I did this for my even older 3rd gen iPod, with a 64GB SDXC card. This is the SD-to-CF adapter I used

http://www.amazon.com/DIGIGEAR-SLIM-CF-Adapter-WiFi-SD/dp/B00XO2KSEO

My "flash-enhanced" iPods work quite well, with over 50GB of songs loaded. I replaced their batteries too, so they are working better than new. 32GB would have been a safer bet (closer to original capacity), but I wanted to fit my complete music library, so I took a chance with 64GB.

The most likely cause is a faulty hard drive. Did you do a Reset (restart) as described in this document?

Learn how to reset your iPod - Apple Support (see section iPod with a click wheel)

If it continues to restart on its own, see if it goes into Disk Mode

Putting iPod into Disk Mode - Apple Support

If it goes into Disk Mode, connect it to your computer with iTunes NOT running. If iTunes picks it up, it may prompts you to do a Restore, which erases the iPod. If you can get it to appear on your computer (outside of iTunes) as a USB storage device, you may be able off-load your songs.

It appears only in iTunes, not in Finder.

If iTunes is running, the iPod only appears in Finder when iTunes is actively syncing the iPod, or if Enable disk use is turned ON in the iPod's Summary settings (or it's currently in Disk Mode). If the Restore fails or it is still corrupted after doing a Restore, there's a good chance the hard drive is faulty.

There is one other thing you can try. But do not do this with your iPod, if you want a chance at off-loading its music. With iTunes NOT running, run Disk Utility. Does the iPod appear in the Disk Utility sidebar? Put it in Disk Mode, if necessary. If you can get it to appear in Disk Utility, you can try reformatting (erasing) the iPod using Disk Utility. You need to do this in a particular way. Here's how to do it using the re-designed Disk Utility that was released with El Capitan (OS X 10.11). If you are using an earlier OS X, Disk Utility works differently; please post back.

Select the iPod device in the Disk Utility sidebar. Select the device, not the volume indented below the device. To the right, click Erase. Set the Erase setup pane like this

Name: [does not matter]

Format: OS X Extended (Journaled)

Scheme: Apple Partition Map

If you have other external storage devices connected, confirm you have the iPod selected in the sidebar. Click Erase button. It should take less than a minute to complete. If the process hangs or errors out, the iPod's hard drive is probably bad. If it completes successfully, quit Disk Utility. Run iTunes. iTunes may not prompt you to do a Restore, but you need to do a Restore because the iPod does not have any of its onboard software after erasing in Disk Utility. Hopefully, the outcome is better.