Vista dual monitor support strangeness - D820

I'm on a Dell Latitude D820 with the Quadro NVS board. Vista Ultimate.

I frequently use dual monitor. Occasionally, when I disconnect the external monitor, the screen on the laptop goes black... except for the cursor! I can see the mouse cursor, but the rest is completely black. If I turn on the 2nd monitor, I get the same effect also on the second monitor. Dual monitor, both black, but the mouse cursor displays fine on both.

I eventually have to do a hard reset to solve this, turning off the laptop.

When I do it, by pressing the on/off button, the screen lights up, showing my windows, and then... it shuts down.

This is driving me nuts.

Note:

- I have always updated AV, Defender, and anti-spyware software

- I have all the updates installed, and the most recent dell drivers

Any help would be greatly appreciated.