If your device can't be recognized by a computer, pls try the following tips to fix it:
1) Try to find another USB cable to connect the device with the computer;
2) Connect it on another USB port (Usually it has several USB ports on the front and back side of the main engine on a desk-top computer )
3) Try to connect the device with another computer if possible;
4) Make a factory reset;
5) Connect the device with the computer after the battery was drained off and powered off automatically.