VGN-SZ740 : No Hard Drive Detected

I have a Sony VAIO VGN-SZ740 (N7) that is a client's computer, and recently their hard drive began to exhibit issues. I pulled the hard drive out of the laptop, backed up the entire hard drive via Norton Ghost using an enclosure (I had to tell it to skip bad sectors), and then replaced it with a new hard drive. Initially, the new hard drive was detected, but now the laptop is not seeing the new hard drive (or the old hard drive). When I go into the BIOS settings, it says "Hard Drive: NONE"

I followed the procedures to remove and replace the hard drive pretty much to the letter, except that when it told me to disconnect the SATA cable from the hard drive, I found this impossible to do in such a narrow confined space and instead disconnected the SATA cable from the motherboard.

Initially, I thought maybe I had damaged the SATA cable, so I ordered a new one from Sony, but even after connecting that cable to the motherboard and hard drive, the laptop still isn't detecting the hard drive. I'm assuming at this point there really isn't anything to do except send it in to Sony for repairs (possibly having them replace the motherboard), but I figured I'd post here first to see if anyone had any suggestions on something else to try.

I'd be happy to provide any further information if needed, just let me know. Any help is greatly appreciated. Thanks!