Are you trying to charge your Apple iPad Wifi or 3G via USB port on your PC that runs Windows XP, Vista and 7 OS but happened that your iPad 3G or Wifi is not charging?
Relax, this is not a hardware failure issue, there is no thing to worry about,
This is due to the USB ports low power source on most of the Windows operating systems.
There is a solution for this, a simple driver update will fix the problem.
Just download one of these BIOS USB driver updates for your PC then installed it.