“USB Device Not Recognized” sounds like your flash drive or mouse just died. Usually it did not. The message is Windows throwing up its hands over a port that has gotten stuck, and the cure is often embarrassingly quick. Try the fixes in order and most people never reach the bottom of this list.
The obvious two that still matter
Move the device to a different USB port. Ports fail one at a time, so the one you always use may be the dead one while its neighbor works fine. Then test the device in another computer if you can. Those two swaps split the problem cleanly: if it works elsewhere, the fault is your PC, and if it fails everywhere, the device itself is gone and no amount of fiddling on your end will save it.
The power-cycle trick
This one fixes the error far more often than it has any right to, and almost nobody tries it. USB ports run on a trickle of power that can latch into a confused state, and a normal restart does not always clear it because the board never fully loses power. So you drain it properly.
- Unplug the USB device and shut the computer down fully.
- On a laptop, unplug the charger and, if the battery comes out, take it out. On a desktop, switch off the wall socket.
- Hold the power button down for thirty seconds with no power connected. This bleeds the last charge out of the board.
- Plug back in, boot up, and try the device again.
That thirty-second hold is the part people skip, and it is the part that works. It forces the USB controller to start fresh instead of waking up in the same stuck state it went to sleep in.
Reset the driver
If the port is still refusing, hand the driver back to Windows. Right-click the Start button, open Device Manager, and expand “Universal Serial Bus controllers.” You may see a device with a yellow warning triangle, which is Windows pointing at the exact thing that is unhappy. Right-click it, choose Uninstall device, then restart. Windows rebuilds the USB drivers from scratch on boot, and a corrupted driver was often the culprit.
The setting that kills ports to save power
Here is the sneaky one. Windows has a feature called USB selective suspend that powers down ports to save battery, and on some machines it powers them down and forgets to wake them back up. Devices then drop out at random, which looks exactly like a hardware fault.
Turn it off and see if the dropouts stop. Search for “Edit power plan,” click “Change advanced power settings,” expand “USB settings,” then “USB selective suspend setting,” and set it to Disabled. On a laptop this costs you a sliver of battery life, which is a fair trade for ports that stay awake. If a device works in another machine but keeps quitting on yours even after all this, the port hardware may be worn, and that is a repair-shop question rather than a settings one. For the wider goal of a machine that behaves, how to fix a slow computer is the place to keep going.