New hard drive cable for my x51

I have an x51. the existing hard drive fails the smart test and wont always boot up.  So i ordered a hybrid hard drive from Dell.  i also bought the premium alien respawn and did the bootable backup, the data backup, and the full system backup on my external hard drive.  but none of these programs will load onto the new hard drive - i think maybe none of these programs recognize that its a new drive so they arent formatting it?  the bios does recognize the new drive.  I have tested both hard drives in the preboot test and they both fail the short self test with similar error codes.  So i called and it was suggested that the connection to the motherboard might not be reliable, or the motherboard itself might not be reliable.  

So i would like to buy  new cable that connects the motherboard to the hard drive - this cable says its a sata2 cable.  What is the part number for this cable and what does it cost?

Ed Mullen