I put my hard drive with windows 7 already installed into a dell optilex 760, but when I turn it on it gets to the 'starting windows' screen but then reboots itself! I then tried to boot from CD drive with my windows 7 disk but it tells me the selected boot device not availble - strike F1 to retry boot, F2 for setup utility Press F5 to run onboard diagnostics. I have no idea what to do next! Thanks for reading.