My screen is whiting out what can I do to restore this?

Hi, is it an occasional thing, or all you get is a white screen?

If 10.7.0 or later...

Bootup holding CMD+r, or the Option/alt key to boot from the Restore partition & use Disk Utility from there to Repair the Disk, then Repair Permissions.

If that doesn't help Reinstall the OS.