Dell D630, when docked,  screen black after boots into Windows 7 Ultimate

Operating a Dell  D630 (8 GB Memory, 1 TB hard drive) with Windows 7 Ultimate.
When undocked , the laptop screen functions normally.
When docked and using a VGA monitor, after Windows 7 logon, the monitor screen goes black (but active).
Same condition as above but boot in safe mode, and laptop & monitor functions normally.

Is this a windows problem or a docked Dell problem?
Is there a solution?

This started after I undocked a operating laptop and tried to connect to an external RGB (not through dock) at another site.
No signal recognized on RGB monitor.
After shutdown and return home, placed in dock, booted, and unable to see anything on home monitor.

Suggestions/solutions greatly appreciated.
John