Do you have another computer or cable to try to see if its the computer or the cable?
My brother had one of these and it had some issues. He fixed it by using a powered usb hub to power the device. For some reason his computer was able to connect and charge it, but communications wouldnt work until powered by an alternate device, so his power supply was probably enough to charge it, but when it was having to be powered and communicate, that drawed a few too many milli-amps and th connection wouldnt be made.