11-18-2014, 04:41 PM
When installing Yosemite or Mavericks, a Recovery Disk is installed. That is the first step when installing Mav/Yosemite, I believe, so it should be there and available on the problem Mac. It's the replacement for the OS on a DVD.
To get to it, hold Cmd R at the startup sound. Then chose to reinstall the OS.
Second question regarding the use of another Mac: The best way to solve that is to start the problem Mac in Target disk mode (hold T at startup sound), and connect it to the good Mac via Firewire. Now the good Mac can install the OS, repair Disk, and do every thing but prepare dinner to the problem Mac.
To get to it, hold Cmd R at the startup sound. Then chose to reinstall the OS.
Second question regarding the use of another Mac: The best way to solve that is to start the problem Mac in Target disk mode (hold T at startup sound), and connect it to the good Mac via Firewire. Now the good Mac can install the OS, repair Disk, and do every thing but prepare dinner to the problem Mac.