Imac running Lion has white screen

Have a client that has an iMac that all of a sudden has a white screen.  We have an image of the boot partition on external drive which starts up fine and you can see the screen so the actual screen is fine.  We have restarted the unit several times and you see the apple logo and it appears to even go through the startup.  I can vnc into the machine and you can see the desktop and use it, but the actual screen remains white.  Does anyone know what causes this, I would prefer not to have to wipe it out and reinstall Lion.  (The backup image is too old to use)

Thank
Peterson50Asked:
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Zephyr ICTCloud ArchitectCommented:
Did you try starting the iMac with following key-combinations?

- Press D during startup = Start up in Apple Hardware Test (AHT)
- Press Option-Command-P-R until you hear startup sound a second time. = Reset NVRAM
- Press Shift during startup = Start up in Safe Boot mode and temporarily disable login items.
- Press Command-V during startup = Start up in Verbose mode.

Maybe the Verbose mode gives more information?
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Peterson50Author Commented:
Which folder contains the display driver, I'm thinking it may be a splashtop driver issue or logmein.  I doubt it is hardware as I can start the computer from an older boot drive and also boot into recovery partition and even vnc into it with the white screen.  I'm thinking it is loading a video driver that conflicts somehow.
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strungCommented:
Try following Spravtek's advice first, in particular resetting the PRAM and trying a safe boot and let us know what happens..
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Peterson50Author Commented:
I did reset of PRAN and SMC, no change will let know after safe boot
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strungCommented:
Also, try disconnecting all external peripherals.

Also reset SMC:  http://support.apple.com/kb/HT3964
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