I have a Mac Pro 2.93ghz Quad-Core Intel Xeon, A1289, EMC2314, 640gig, 8gig ram, and am trying to install Yosemite or Mavericks. After starting the installer the hard drive where the install goes is not showing up. I did install 10.6. just fine to upgrade. I formatted the drive and even used a different hard drive to no avail. I have both programs on a usb stick and are tested to work. I have an identical Mac Pro and did the install without a glitch. Today I've installed Mavericks on the second identical computer again using the other ones hard drive. It installed fine and runs well on the second Mac. Than I put that drive into the problem Mac but it will not start up. Then I booted the computer with the system disk and opened the start up window. The drive shows 10.9. as start-up but will only boot to the Apple screen with the rotating wheel and loops. Any ideas?