I had a HD crap out on me once, and I know that it didn't sound the same as when it worked. It made a clicking sound about every .5 seconds. Also, my buddy's did the same, but rather than clicking, it just sounded like the bearings went bad and made this loud kinda grinding/vibration sound.
If yours sounds the same as it always did, then I would check the cable to the hard drive, or however it connects to the laptop's motherboard. I have had IDE cables come loose before and the computer said the same thing yours did, "Hard drive not recognized" or some s**t. I took the cover off, tightened up all the connections, and VOILA, back in business. Try it out before dropping a few hundred on a new drive bro. Good luck...!!!