Some users have reported that their iPad does not charge when connected to their PC. This is normal for PCs and older Mac computers. The power requirements of the iPad are fairly high; and most computers don’t provide enough power via their USB ports to be able to charge the iPad (first or second version). Apple states that the best way to charge the iPad battery is to connect the iPad to a power outlet using the included Dock Connector to USB Cable and 10 W USB power adapter. When you connect iPad to a USB 2.0 port on a Mac with the Dock Connector to USB Cable, the iPad may charge slowly while syncing.
There are some applications (e.g. ASUS Ai Charger) for PCs that can charge an iPad by pushing more energy through the USB to properly charge the iPad. However, we advise caution with respect to using this program, since several people have reported system instability issues with this, and for others it simply didn’t work.