You plug something in and Windows announces that the last USB device malfunctioned and was not recognised. It is one of the least informative error messages in the operating system, and the causes behind it are few enough to work through quickly.
The short answer
Try the device in a different port, ideally a rear port on a desktop, and try a different cable. Those two rule out the most common causes in a minute. Then rebuild the USB stack by uninstalling the root hubs in Device Manager and restarting, which resolves most of the remaining cases.
What the message actually means
Windows attempted to identify the device and the process failed. That can happen because the device is not getting enough power to complete its startup, because the data connection is unreliable, because the driver is missing or corrupted, or because the device itself has failed. The message does not distinguish between them, which is why a systematic approach beats guessing.
Try a different port
On a desktop, use a rear port, which connects directly to the motherboard rather than through a front panel cable. Front panel ports are a common weak point and are often not connected as well as they should be.
Try a different cable
Cables fail internally and charging-only cables have no data connection at all. If the cable came bundled with something else, it may not be a data cable. This is a very common and very quick thing to rule out.
Remove any hub or adapter
Connect the device directly to the computer. Unpowered hubs cannot supply enough current for drives and anything with a motor, and cheap adapters fail in exactly this way.
Test the device on another computer
If it fails everywhere, the device or its cable is at fault and you can stop troubleshooting the computer.
Rebuild the USB stack
In Device Manager, expand Universal Serial Bus controllers, uninstall every USB Root Hub, and restart. Windows reinstalls them on boot. This is the single most effective software fix.
Turn off USB selective suspend
In advanced power settings under USB settings, disable selective suspend. It powers down ports to save energy and causes devices to fail to initialise, particularly on laptops.
Clear the power management checkbox on each hub
In each USB Root Hub’s properties, power management tab, clear the option allowing the computer to turn the device off to save power.
Update the chipset drivers
From your motherboard or laptop maker rather than Windows Update, which often ships older versions. USB controllers are part of the chipset.
Do a hard power drain before anything more involved: shut down, unplug the power, hold the power button for thirty seconds, then start up. On a laptop remove the battery if it is removable. This clears a latched state in the USB controller and it resolves a surprising number of cases in two minutes.
Power is the usual culprit
Devices that draw meaningful current are the ones that produce this error most: external hard drives, anything with a motor, some webcams, and devices that charge while connected. A port supplies a limited amount, and a device that needs more than it gets fails partway through starting up, which Windows reports as not recognised.
The signs that point here: the device works on a desktop but not a laptop, works on one port but not another, or works through a powered hub but not directly. In all three cases the device is fine and the power budget is the limit. A powered hub with its own mains adapter is an inexpensive permanent fix.
Be careful with unbranded USB devices and cheap hubs. A poorly made device can draw more than a port is designed to supply, and the computer protects itself by shutting the port down. Repeatedly triggering that protection is not good for the controller and can eventually damage it.
When it is one specific device
- An external drive. Almost always power. Use a Y-cable drawing from two ports, or a powered hub.
- A phone. Check the cable is a data cable, and check the phone is not set to charging-only mode. Phones ask what the connection is for, and the answer defaults to charging.
- A printer or scanner. Often needs its own driver installed before it will be recognised properly.
- A device that worked yesterday. Something changed: a Windows update, a driver update, or the cable got bent. Check the update history.
- Everything in one port. That port has failed. A powered hub in a working port solves it cheaply.
USB-C specifics
USB-C ports vary enormously in what they support even on the same machine. A port may carry data, power, video, or any combination, and they look identical. Check the small icons beside each port before concluding a port is broken, because a device plugged into a power-only port will behave exactly as though it were faulty.
What does USB device not recognised actually mean?
Windows tried to identify the device and failed. That covers insufficient power, an unreliable data connection, a missing driver, or a failed device. The message does not distinguish between them.
Why does my external drive work on a desktop but not my laptop?
Power. Desktop ports typically supply more current, and a laptop port may not meet what a spinning drive needs at startup. A powered hub solves it.
Can a cable cause this?
Frequently. Cables fail internally, and charging-only cables have no data wires at all. Swapping the cable is the quickest thing to rule out.
What is USB selective suspend?
A power-saving feature that switches off idle ports. It causes devices to fail to initialise, particularly on laptops, and disabling it is a common fix.
One port has stopped working entirely. Is it worth repairing?
On a laptop the port is soldered to the motherboard, so it is a board-level repair. A powered hub in a working port is usually the sensible answer instead.
The bottom line
Try a different port and a different cable first, since between them they explain most cases and both take a minute. Do a hard power drain, then rebuild the USB stack in Device Manager and turn off selective suspend. And if the device draws real power, suspect the power budget before anything else, because a powered hub fixes what looks like a broken device.
