ok lets see if i can help you...before following the given steps try using different ports of USB...first unplugged your USB than restart your PC and attach USB in different port.

If still didnt work than do the following steps:

Step 1: Right click on your my computer Icon
Step 2: then click on Properties
Step 3: after this find Hardware tab(if you are using XP) and click on it
then click on Device manager
or else if youy are using windows 7 there will be Device
Manager option in left column of opened file..
Step 4: Now find from the list the Universal Serial Bus Controller
Step 5: uninstall the Universal Serial Bus Controller item i.e
Enhanced host Controller which you can do by right
clicking and then clicking Uninstall
Step 6: Once you have uninstalled , Restart your PC and attach your USB in
port it will automatically install the required driver.

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Regards,
~ Riz ~