Usually something small. Codee 2.0 is assembled with the screwdriver in its box — no soldering — so the checks are quick.
1. Charge it first. Codee has a LiPo battery inside; plug it in over USB for a full hour and try again. A battery that arrived flat looks exactly like a dead pet.
2. Check the battery connector and the screen connection against the build-guide photographs at circuitmess.com/blogs/resources. Both need to be seated fully and squarely. If the screen ribbon looks loose, do not press or re-seat it by feel — photograph it and include that in your email; the careful way to handle it is covered in Attaching the Codee 2.0 screen without damaging the ribbon.
3. Restore the firmware from code.circuitmess.com on a desktop computer running Chrome, Edge or Opera. A white or frozen screen after coding is usually the program rather than the pet, and restoring puts Codee back to how it shipped.
Still dark or white? Email us with your order number, photos of the board and the screen connection with the casing off, and a short video from power-on.
Email that to [email protected]. We look at each case individually, and if a part turns out to be genuinely defective, replacing it costs you nothing — see Do your kits have a warranty?
If the restore itself will not run — the browser cannot see the device, or it stops part-way — see The firmware restore at code.circuitmess.com fails or cannot find my device.