my ipad is not charging with 10W usb power adaptor ? what are the causes?

My Ipad is not charging with the 10 W USB Power Adaptor Charger ? Please tell me .....What can be the issues with solutions to resolve them ? Even when the USB is connected to computer it is not charging , however , the transfer of data is taking place including Sync. Is there a problem with the charger or the ipad please isolate & inform. Thanks.