Are your USB ports enabled in your BIOS?
What kind of computer (notebook or desktop)? What operating system (Windows 7, Vista, XP, etc)?
Are you using any other USB devices successfully?
Does the USB storage device require external power? If so, is it attached?
Have you tried the USB storage device with another computer? Have you tried different USB ports and/or a different USB cable?
Please clarify and I am sure someone can help. Good luck!