Thinkpad 600 (No video on screen) black screen?

I have a used thinkpad 600-2645 that has no video unless connected to an external LCD. Previous seller tried a replacement LCD but still no luck. Currently, system has no OS. Does anyone have a suggestion on how to repair. I'm uncertain if this is a common problem or one that can be easily corrected. Your help is greatly appreciated.

Thanks

Angela
November 2006