Fixing a Mac White Screen or Not Booting

Failure to Boot on a Mac, White Screen of Death...

Had a few friends who have run into a white screen on bootup for their Macs after dropping it or having a power failure.  Rather than have to send in for repair (time + money), a much easier fix is detailed at The Pabster's Notebook.
The basic idea is that the Hard Drive boot sector got corrupted, but the Mac continues to try to boot from it.  The system disc doesn't help because the OS doesn't try to boot from anything else unless the hard drive is first disconnected.
Once that is done, you can boot off the installation disc and then use the Utilities > Disk Utility to repair the hard drive.
You might have to also switch default bootup to the installation disc first under Utilities > Startup Manager so you can restart and reconnect your hard drive when the power is off.

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If Disk Utility is not enough to repair the drive, as was the case a few times when I've tried to repair, you'll want to look up DiskWarrior to boot with and repair the drive.  If the only computer available to burn the disc with is a Windows (usually for me), you'll want to use TransMac to burn the dmg file.