Dual monitor problems

[Oliver Elphick <olly@lfix.co.uk>]

I am trying to use two monitors at once, for the first time, using an 
Nvidia dual head card.

I have now got the two monitors displaying a single screen and the mouse 
passes from one to the other.  However, the second screen blanks after 
around 20 seconds of non-use and nothing will bring it back to life.  I 
can pass the mouse into it, or select a  window that is on it, but it 
remains black.  The only exception is that it will restore when the 
screen is locked and I enter my password to unlock it.

Where should I look?

Debian version: sid, recently updated

Oliver Elphick