Problems charging your iPad when it is connected to your computer,
While your iPhone or iPod may not have a problem charging via the USB port on your computer, the iPad requires considerably more power. This means some USB ports, especially those on older computers, simply don't have the juice to get the job done.
So how do you know if your iPad is charging? If your the port has enough power to charge the iPad, a lightning bolt will appear in the middle of the battery meter on the upper right-hand side of the iPad. If it doesn't have enough power to charge the iPad, you'll see the words "Not Charging" next to the battery meter.
Oftentimes, the iPad can still be charged using the computer if you put it in suspend mode while it charges. However, if the computer is powered off or goes into suspend mode, the iPad will not charge.
The easiest solution is to plug the iPad into an electrical outlet using the adapter that comes with the iPad. This is also the fastest way to charge the iPad. Even computers that can effectively charge the iPad won't put out nearly as much juice as an outlet.
Problems charging the iPad when it is connected to an electrical outlet
First, make sure the iPad doesn't have a software problem by rebooting the device. To do this, hold down the suspend button at the top of the iPad. After a few seconds, a red button will appear instructing you to slide it to power off the device. Let it power down completely, and then hold the suspend button down again to power it on. You'll see the Apple logo appear in the middle of the screen while it boots back up.
If the iPad still will not charge through the electrical outlet, you may have a problem with the cable or the adapter. You can quickly find out if you have a problem with the cable by connecting the iPad to your computer. If you see the lightning bolt on the battery meter or the words "Not Connected" next to the battery meter, you know the cable is working.
If this is the case, simply buy a new adapter. If the iPad doesn't respond when you connect it to the computer or when you plug it into the wall, you probably have a bad cable, which can also be easily replaced.