My late 2011 MacBook Pro was not recognizing any internal drives so I thought at first that maybe my hard drive had been fried. I took the hard drive out after reading forums on Mac's website and decided to use an external enclosure to plug in my hard drive. It worked and my MacBook Pro booted from the external drive. I narrowed the problem down to being the hard drive cable. With my warranty gone, the repair could have cost me upwards of $120 if I took it to the Genius Bar. I came to iFixit.com and found the cable used for $35. Saved myself a lot of money.
The repair was straightforward. Carefully remove the faulty cord and replace it with the working one. Then install the internal drive again and boot up the laptop. Start up may take a while longer the first time as the laptop recognizes to again boot from the internal.
Always check the Mac forums and see if you can repair it yourself before taking it to a Genius Bar. I don't mean digging your hands around the laptop as that could terminate your warranty (if you have one). Educate yourself of the problem and if it seems simple, go for it.