Some devices require a minimum output from the charger in order for them to start charging.
If your device is not charging from your PC's USB port, the USB port is probably not putting out enough power for it to register on the tablet.
I purchased a charger from Amazon that works with my iPad2 and all my devices, tablets cell phone etc.
When i get back to my laptop I will post a link to it, it cost about 10.00 but it has been worth it for me, it will probably do fine for you as well.
Hope the OP hasn't purchased one yet. These tablets are not designed to charge via USB. Dig thru my posts and you will see pics of the various chargers that DigitalGadgets use for their tablets.