buffer i/o error on device hdc,logical block 0 (imp)
 

dear all
i am using a harddisk which is 80GB Samsung on which my Linux (Fedora -3 ) is installed.
i have attached one more external harddisk which at first time showed me on hdc , i worked on it but suddenly it is not detecting the external harddisk.
it is giving an error of

end_request:i/o error,dev hdc, sector 0
buffer i/o error on device hdc,logical block 0

i have all my backup on that external harddisk,i dont have an idea how can i do this now.pls help me out ...........

its very urgent for me