Check whether the device is recognized on another computer. If not, try replacing the USB cable – it is possible that there was a fracture of conductors. If the replacement cable did not help, the machine may require repair or replacement.
One cause may be static electricity on the metal plug of the device or in the USB connector of the system unit. Remove the device from the slot and turn the computer off for 2-3 minutes, completely disconnecting it from the power source. If possible, carefully blow out the USB connector – has accumulated inside the dust holds electrostatic charge.
The system may fail to recognize the device due to a driver failure. To remedy the situation, delete the file INFCACHE.1, which contains information about drivers for USB devices. To do this you need administrator rights.
Open the folder C:\Windows\. In menu "tools" click "folder options" and go to the tab "View". Under "Additional options" check "Display contents of system folders" and uncheck option "Hide protected operating files". Select "Show hidden files and folders".
Expand the folder C:\Windows\inf\ in Windows XP or C:\Windows\System32\DriverStore\ in Windows 7. Locate the file INFCACHE.1, right-click it and choose "Uninstall". Connect the device and install the driver again.
May have been a corrupted driver USB controller of your system unit. In the control panel, expand Administration and then double-click "computer Management". In the right part of the window, double click open "device Manager".
In the new window, click on the "+" icon to the left of "universal serial bus Controllers USB". In the list, right-click on each device and choose "Delete" from the context menu. After reboot the system should automatically find the correct driver. If necessary, install them yourself.
If reinstalling drivers doesn't help, maybe the USB controller has failed. You can buy a USB hub and install it in the PCI slot.
In addition, the reason for the failure of the USB port may become insufficient food. If you use an all ports power weak power supply may not be enough. In this case, will disabling 2-3 devices in device Manager.