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Try booting up our Mac into Safe Mode, by pressing and holding the Shift key while it boots. Release the Shift key when the Apple logo and progress bar appear. To leave Safe Mode, just reboot your Mac without holding the Shift. See if your Mac works now. Your Mac automatically checks the directory of your startup disk when you start up in safe mode.
Another option is to try and start up in Recovery Mode by pressing and holding the Command + R keys and then use Disk Utility to repair your startup disk.
AppleToolBox also has an article about this exact issue: (https://appletoolbox.com/2014/09/mac-fix-white-screen/)