mount an extenal usb hdd

hi everybody i think i did a misstake and now i need help. i try to explain my problem i recently upgrated to 7.04 feisty and on fooling around  a bit  trying to set rw priviliges .  i  unmount  my  external  usb  ntfs  hdd. i am very attached to this drive because all my files are there and i use it to transport and use the contents between diferent windoze boxes and my ubuntu-laptop. now i try to remount and it  doesnt. help please...