Windows 7 - Disk check could not be performed because windows cannot access disk

HI, i have a Transcend StoreJet 25M 640GB external hardisk, at first it was working properly until a time that it wont open.
at first it will ask me to format the disk to be able to open it or sometimes it will say ” NOT accessible : the parameter is incorrect”
i did some searching and i learned that i need to chkdsk it, and when I did using command prompt it says ” Data error (cyclic redundancy check)”
if a click properties on external hardisk , it has zero bytes free and used space, and if click the “check now” in tool tab under error checking it says ” The disk check could not be performed because windows cannot access the disk..
is there anything i can do the fix these ?? and be able to operate my external hard disk again? please help me , I would really appreciate.. thank you (forgive my grammar)

Try the Recovery tool from here:
http://www.transcendusa.com/

Before you try the recovery tool already mentioned, check to ensure your connections to the external drives are ok. I had the same problem and wiggling the usb cable did the trick. Good luck!

Snarks