We have an old iPod that was working for a long time but has suddenly started displaying the sad face and refusing to boot. Because I am a nerd and I like to fix 13-year-old things, I poked around the interwebs to see if there was a replacement hard drive I could install. Apparently they stopped making hard drives for this iPod about 5 years ago, because my usual go-to parts resource had none. I then stumbled upon an Instructable which claims I can replace the drive with a Compact Flash card using a CF to SD adapter. Amazon Prime had one for $7, and I have an old 4GB CF card laying around that I can test with, so that was a no-brainer. After following the directions and adding a CF card through the adapter I’m still getting the sad folder icon–so it might be time to replace the battery.
Update: New battery, same problem. I think this thing is toast.