First, the computer cannot recognize the USB device.
The second is that the USB device cannot be recognized by the computer. We must first determine whether it is a computer problem or a USB device problem. We can use other USB devices to test the computer for problems.
If it is a computer problem. Is your computer damaged by a virus? Is the USB2.0 driver installed intact or incompatible version? Is there a software conflict (solve the software problem first) Generally there is a prompt to install the driver.
If it is a computer hardware problem. We first use a multimeter to measure the four lines of USB (red + 5V white DATA-data-green DATA-data-black ground). Multimeter red test lead to black test lead (white and cymbal. The resistance value is not different by 50 ohms These two lines are from the south bridge. If the resistance value changes too much, it can be judged that it is a south bridge problem. It means that the USB module inside the south bridge is burned.
Looking at the outside USB devices now have many drivers. Even if there is no driver, it will not appear unrecognized. There are several unrecognized situations. A USB data cable is not connected or has poor contact. Generally, it touches that place because it may be rusty or swollen inside for a long time, or it may be blocked inside. Two USB cables are not working. There will be no response if the red line is not connected, and the white line cannot be identified. The green line is unrecognizable. The white and green lines cannot be reversed. It is also unrecognizable. The black line is not connected and there is no response. This measurement method has been mentioned above.