Please check the followings:
- Use the USB cable supplied with this unit. Sometimes you cannot charge the unit via another USB cable. Be sure to use the USB cable supplied with this unit.
- Check that this unit and the computer are directly connected, not via a USB hub.
- A problem may occur with the connected USB port of the computer.
Connect to another USB port if it is available.
- This unit may not be charged at low temperature or high temperature. Charge this unit between 5 and 35 degrees.
- Sometimes the indicator(red) is not lighted after you don't use this unit for a long time, because the rechargeable battery is depleted. Continue to charge this unit, then the indicator will be lighted after a few minutes.
- Check that the computer is turned on because you can't charge when the computer is in standby, sleep or hibernation mode.
Try the USB connection procedure again to identify the issue.