What Does This Error Mean?

Micro:bit not showing as a USB drive is almost always caused by using a charge-only USB cable instead of a data cable. Try a different cable that is confirmed to support data transfer — many cheap micro-USB cables carry power only.

Affected Models

Micro:bit V1
Micro:bit V2
Micro:bit V2.21

Common Causes

Charge-only USB cable — no data pins connected inside the cable
USB driver not installed on Windows (DAPLink driver required)
USB port on the computer is defective or underpowered
Micro:bit firmware is corrupted — appears as an unrecognized device
USB hub without power delivery preventing Micro:bit from enumerating

How to Fix It

Try a different USB cable.

This is the most common fix. Use a cable you have confirmed works for data transfer with another device (such as syncing an Android phone). Many cheap micro-USB cables are power-only and will charge the Micro:bit but never show it as a drive.
Connect directly to the computer, not a hub.

USB hubs (especially unpowered ones) can fail to provide enough power or signal quality for the Micro:bit to enumerate. Plug the Micro:bit directly into a USB port on the PC or laptop.
Install or update the DAPLink driver (Windows).

On Windows, the Micro:bit requires the DAPLink (CMSIS-DAPv2) driver. Open Device Manager and check if there is an unknown device when the Micro:bit is plugged in. Download the latest driver from the official Micro:bit website (microbit.org) and install it.
Reload the Micro:bit firmware.

If the Micro:bit appears in Device Manager as an error device even with a good cable, the DAPLink firmware may be corrupted. Hold the reset button on the back of the Micro:bit while plugging it in — it should appear as 'MAINTENANCE' drive. Download the latest firmware .hex file from microbit.org and copy it to the MAINTENANCE drive.
Test on a different computer.

Plug the Micro:bit into a different PC with a known-good cable. If it appears correctly on the second computer, the USB port or driver on the first computer is at fault. If it fails on both, the Micro:bit itself has a USB hardware issue.

When to Call a Professional

If the Micro:bit shows as an unknown device in Device Manager after trying multiple cables and installing the DAPLink driver, the Micro:bit's USB controller may have failed.