What the error means — and what usually causes it
The notification is Windows reporting that enumeration failed: the controller could not read the device descriptor, the small data block every USB device sends when plugged in to say what it is and how much power it needs. The full message — “The last USB device you connected to this computer malfunctioned, and Windows does not recognize it” — sounds fatal but rarely is. In Device Manager (devmgmt.msc) the failed entry usually shows as “Unknown USB Device (Device Descriptor Request Failed)”, often with status Code 43.
The causes are boringly predictable. Bus-powered hard drives and unpowered hubs draw more current than the port can give, cables break internally or turn out to be charge-only, and after sleep or a “shutdown” with Fast Startup enabled the controller can wake up in a broken state. Only a small minority of cases involve actually dead hardware.
- Insufficient power — an unpowered hub feeding a bus-powered hard drive is the classic victim
- A damaged or charge-only cable with no working data lines
- Code 43 in Device Manager — the driver itself reported the device as failed
- USB selective suspend putting the port to sleep and never waking it properly
- Fast Startup leaving the controller half-initialized after a normal “shutdown”
- Outdated chipset or USB 3.x controller drivers, typically after a big feature update
Quick fixes first: ports, cables and a real restart
Rule out the physical layer before touching any settings. On a desktop, plug the device into one of the rear ports soldered directly to the motherboard instead of the front panel; on a laptop, try the other side. Swap in a known-good data cable — charge-only Micro-USB and USB-C cables are the single most common hidden cause — and unplug other USB devices, hubs first.
Then do a real restart. Clicking Start → Power → Shut down does not fully reset the hardware when Fast Startup is on, so hold Shift while clicking Shut down, or run shutdown /s /t 0 in a command prompt. On a desktop you can also switch the PSU off for a minute to drain standby power; on a laptop, shut down, unplug the charger and hold the power button for 15–30 seconds. A surprising share of cases ends right here.
Fixing the USB stack: Device Manager, drivers, selective suspend
Open Device Manager (Win+X → Device Manager) and find the failed device, usually under “Other devices” or “Universal Serial Bus controllers”. Right-click it → Uninstall device, then Action → Scan for hardware changes. If the error returns, uninstall every entry under “Universal Serial Bus controllers” — the root hubs and host controllers — and restart; Windows rebuilds the whole USB stack from scratch on boot.
Two settings stop the problem from coming back. First, install current chipset drivers from your motherboard or laptop maker, and check Settings → Windows Update → Advanced options → Optional updates → Driver updates. Second, in Power Options (powercfg.cpl) open the advanced settings and set USB settings → USB selective suspend to Disabled — with it off, ports stop falling asleep in a broken state. For high-draw devices, use a powered hub rather than chaining them off the PC’s own ports.
Questions and Answers
Why does Windows say USB device not recognized when nothing is plugged in?
A failing port, a hub left connected, or an internal device such as a card reader keeps failing to enumerate. Open Device Manager, look for the unknown entry, and unplug non-essential devices one by one until the culprit stops retrying.
How do I fix unknown USB device Code 43?
Uninstall the device in Device Manager, restart fully, and update the chipset and USB controller drivers. If Code 43 follows the device to another port and another PC, the device itself — not Windows — is faulty.
Can one USB port fail while the others keep working?
Yes. Ports are wired in groups, each with its own controller channel, so one damaged group or header cable can knock out two ports while the rest work normally.
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