Can't complete my purchase in iBook Store

...for the whole day. I have proceeded through all required steps to chekout hwvr it stopped two times during the time since it started downloading (btw VERY SLOWLY) . The first time the notification poped up requiring me to check for available downloads in the Store. When I did this it seemed it recovered somehow, but not for a long becuase the story repeated again THIS time I saw the notification of "Error 1004". When I tried to check for available downloads it told that all available downloads are completed THOUGH the status line shows the process in the beginning. Please, help me!!!!