Device I/O Error

Hi,

       I have a 250gb external hdd connected to my Dimension 9200 system with Vista Home Premium.  I ahve been having some issues with vista starting up/shutting down, I think that i have narrowed it down to a fault with the external hdd drive, as when I remove it the machine is okay.  I am getting a I/O device error when trying to open the external hdd, and says drive is not accessable.  Is the drive on its way out or is there anything that i can do?  Thanks

Martin