> Try a safe boot. > Run disk utility. > Reset PRAM. > Using terminal in single user mode. > Reinstall Mac OS X. Firstly you need to shut down your computer. Restart and then hold down the "Command-R" keys until you see the OS X Recovery utility screen. Select the disc utility option and select the "First Aid" tab select your hard drive from the sidebar and then click on "Repair" to diagnose and repair the disc. for any other steps visit this blog FIX-mac is stuck on the white startup screen! and see if this help to fix the problem thanks