Make sure the battery has been pushed in all the way. The should be an audible click when it is.
Check the charge light. If it is blinking quickly that means your battery is charging. If the blink is slow or random then it is not. The best way to test this is to remove the battery and observe the blink rate of the charge light then insert the battery to see if it changes. If it does not then there might be something wrong with your modem. Please contact us in this case.