Hi aleuta. Have you tried any other USB devices with your computer? Have you tried different USB ports, and are the USB ports you are using directly on the motherboard or on an extension bracket? If they are on an extension bracket or the front panel, then you may just have a socket loose on the motherboard. Otherwise you may have a problem with the motherboard USB driver chip. Another possibility is that you have fitted another USB device that is overloading the USB chips ability to supply power.