I heard there is a virus going around that hijacks the "Autoplay" files on external drives.....so like has been said, scan the PC for Virus's. Then see if you can find USB 2.0 drivers online. If that doesn't work, check your registry for the setting and see if it is set to 3 vice 4.

HKEY_LOCAL_MACHINE > SYSTEM > CURRENT CONTROL SET > SERVICES > USBSTOR > START > VALUE = 3 .