If the battery on a PRS is totally dead (which it shouldn't be if it's new, but strange things sometimes happen in shipping/storage) there can be problems getting it to charge off of USB. You need to use an AC adapter. These are available from Sony for insane prices, from various third-party vendors at wildly varying prices and levels of quality, and from all of the usual suspects. AC adapters for the Sony PSP portable game console reportedly also work, but I don't have any first-hand experience there. After the frustration of checking every local GameStop for PSP adapters, I just broke down and bought the Sony charger.
I should mention that said Sony charger is rated at 2 amps. Why an ebook reader would need to pull that much current, I have no idea, but that's what the charger can supply. I don't know how dependent it is on having that particular rating.