To charge iPad / iPad 2 / iPad 3 or even new iPad mini / iPad 4 via USB connect the wide end of the included data cable into connector at the bottom of Apple tablet and the narrow end into the nearest USB port on your computer. This may or not may charge when iPad is awake.An older computer does not have enough power to charge iPad when it is awake and you see "not charging" message at the right top of your iPad. Don't panic, change can come quickly and easily. Following is a trick for your iconic tablet:
Press shortly Wake/Sleep button and put your iPad tablet to sleep
That is all. Your tablet will begin charging now over USB. However, this way of charging is not recommended as it deteriorates battery.