Windows App doesn't recognize device - cannot transfer via USB

My device, Samsung Galaxy Tab 10.1, is shown as compatible with ePub format. I followed instructions for transfer of ebook but my Tab does not show up as a device in the DE app on Windows 7. I copied it directly from File Explorer to my Tab as well but neither Overdrive nor any other program on my Tab seems to read it. Is there a workaround or am I doing something wrong?