I just replaced my 500 GB hard disk a day ago and have so far installed a bare minimum applications but my macbook pro (8GB 2012) is stuck at the gray screen with apple logo at the reboot. I have already tried running safe mode but it won't turn on. I tried fsk -fy method too but to no effect. I can still enter into recovery mode and can verify my harddisk and it shows no repair needed. But even when I try to install OS Mountain Lion X again, it says, "There was an error in initiating the install. Please run the application again". Your help will be appreciated.