'''There are some steps to repair white screen on MAC'''
'''1. Try a Safe Boot'''
Mac OS X 10.2 and later Safe Boot includes disk checking and repair. First start your Mac in Safe Mode. To do this, shut down your Mac. Now Turn on your computer by pressing the power key while holding down the Shift key. When you see the Apple logo, release the Shift key. After your Mac fully starts, restart your computer normally without holding any keys/buttons during startup. Note that Safe Boot is slower to boot.
'''2. Run Disk Utility'''
Turn your Mac off by holding down the power button for a few seconds. Turn on your Mac and hold down the Command and R keys until you see the Apple logo. Then you should see a “Mac OS X Utilities” window. Select Disk Utility, click your OS X hard drive and select verify/repair disk.
'''3. Reset PRAM'''
This may fix your boot failure. PRAM (“parameter random-access memory”) stores some of your settings. You may reset PRAM. To do that, turn off your Mac. Now turn on your Mac. Then, immediately, hold down the Option-Command-P-R keys until your Mac restarts. When your Mac is starting up, release the keys.
'''4. Using Terminal in Single User mode'''
Most times, the steps above will usually fix your problem. However if it did not work for you there are a few additional steps that you can take before you decide to Reinstall Mac OS X on your machine.
The first three steps help you launch into the single user mode on your Mac.
Step – A. Shut down your Mac.
Step – B. Press the power button to start up your Mac.
Step – C. Immediately Hold down Command-S for single-user mode.
Now you have launched your Mac on a Single user mode. The next few steps will help check for file system consistency and remount the boot volume.
Step – D. On the terminal window Type fsck –fy and press return
Step – E. Type mount –uw and press return
Step – F. Type touch /private/var/db/.AppleSetupDone and press return
Step – G. Type exit and press return
These Seven steps above should help your Mac deal with the White Screen issue.
'''5. Reinstall Mac OS X'''
If nothing above works, you may try this. Your Mac needs to be connected to the Internet. See number#2 above. Follow the same steps. Restart your Mac and hold down the Command key and the R key until the Apple icon appears; when you see the Mac OS X utilities window, select the Reinstall option.