Currently Being ModeratedAug 20, 2013 4:39 AM (in response to gdaber)
See this Apple note on steps to take when faced with a grey screen on boot.
Taking the logic board out to hook up to another system has nothing to do with the data stored on your hard drive. It's possible they were talking about removing the hard drive to hook up to another system.
After you get past this issue, consider buying an external hard drive and backing up your system on a regular basis.