If the drive is using the USB port to get power, then it may not be getting the required amount from the port you are using.
This could be: bad connection, faulty port power, or to many devices using the port's power than the port can supply power to.
1. Disconnect any other devices from that port and try it.
2. Try using a separate powered hub, if you have one one or have access to one.
3. Try a different port.
4. If, you are using an extended or long length of cable, try a shorter one. You may want to try another cable for the heck of it, anyway.
While the device is plugged in, check in device manager, to see what devices are using the power and on which ports.
Or try using
usbview or
usbdeview to see what is using what and where.
