Win7 can't identify usb device. How to do

Sometimes when we plug a USB mobile hard disk or USB flash drive into the computer, we will encounter the problem of “unrecognizable USB device”. Repeated retry will not help, but the same USB device is in other computers. Medium can be displayed normally. If you encounter this problem, you can refer to the following three methods to solve.
Method 1: Uninstall the driver, then reconnect the external hard drive
Open the Control Panel (small icon view) - Device Manager, find your device in the disk drive list, right click and uninstall.

remove the USB cable, and reconnect, the driver will automatically load at this time, generally return to normal.
Method 2: Reinstall the USB controller.
Open the Control Panel (small icon view) - Device Manager, expand the Universal Serial Bus controller, right click on the device and select "Uninstall", and repeat the above for each device. When you are done, restart your computer and the system will automatically install the USB controller.

Method 3: Disable USB selective suspend setting.
Control Panel - Power Options, click Change Plan Settings next to the currently selected power plan.

click Change advanced power settings.

expand USB selective suspend setting -USB setting, set it to "Disabled" to determine.