I have been building a new desktop and have tried to salvage the Hard Drive from my old build. My new computer currently has a Western Digital 70GB with 7200RPM and is a SATA 3.0, my old Hard Drive is a Western Digital 1TB with 7200RPM and is a SATA 3.0, so obviously I am confused as to why this doesn't work. The new one has Windows 7 Ultimate and the old one has Windows 7 Professional, the only major difference is the new one came in a HP, and the old one is in a Dell, but I couldn't imagine that making a difference. So anyway what happens is I take the new one out and put the old one in and start it up. The system starts up and then the windows logo comes up and begins to animate when it freezes. It then restarts on its own and starts up, but then gives me the start up failure message and asks if I want to start normally or in repair mode. The same thing happens when I put the new drive in the old build. Both hard drives still work in their original builds even after these attempts. Any Ideas?