Dual screen problem

[jm2003uk]

Hi all!

I've just plugged in a second monitor to use as an extended desktop, however it doesn't seem to want to work as one. I can have either monitor working on their own (with the other going to standby) or i can have a mirrored desktop. Selecting extended desktop and pressing apply does nothing at all, other than the display properties window flickering briefly. This happens regardless of whether i use the mint display properties or the ati catalyst control centre (which closes itself when i click apply).

AMD Radeon HD 6700 Series
ATI propitiatory driver (version 8.95?)
Catalyst version 12.2
Control Centre version 2.13

Any suggestions on what to try?