Hi, I was trying to upgrade my hard drive on my 2009 15" MBP 2.53GHz to a 7200RPM WD Scorpio Black 320GB BEKT I had. The WD HD had Leopard on it, but when I swap the HD into the machine and boot it up, the machine just hangs and the Apple sign won't even show up. Then I plug in the original HD to the machine as a external device, and boot up the machine with OPTION key to select OS. It properly show up the partition I had in the WD HD and the external HD. When I click boot from the WD HD, it hangs again. I then switch back the HD and use my original HD to reformat the OS partition I had in the WD HD, then swap the drive back again. I boot it up and enters the Snow Leopard installation disk and begin installation process. It took forever to finish the installation. On my original HD, it only took 21 min. to do a clean install. Now with the WD HD, it took 33 min. to get 10% of the installation process done. I then took out the WD HD and did a surface scan on it, but no bad sectors were found. Is this a compatibility issue? or HD hardware problem.