In the process of troubleshooting a 20" iMac (Late 2006) I reset the PRAM. This somehow resulted in some strange LCD display behavior. Now when I boot the machine the screen initially lights up and displays the grey screen, I hear the usual startup chime, but then after a few seconds the screen goes dark (just about the time the Apple logo appears). The machine otherwise starts up normally and I can see the boot finishing if I hold a flashlight up close to the screen. The screen appears to work fine, the backlight comes on at startup but then shuts off. And it worked fine up to the point when I reset PRAM. What happened when I reset PRAM that would cause the backlight to stop working? How can I restore PRAM display settings so the display will function normally again? What's wrong with my boot.efi? Thanks in advance for any help.