theclouds :
That's okay. The reason I suggested reinstalling drivers was to make sure Windows recognized the card and not a generic display adapter.
Next, I'm under the impression you had the 450 first and aero was working. It was only until the 580 was added that aero quit.
Try using Aero Troubleshooter. Type aero in the search programs and files box, select find problems with transparency and other visual effects.
http://support.microsoft.com/kb/976170/en-us
This will list nearly all potential contributors.
EDIT: If the utility doesn't fix it, list the troubleshoot report and we'll work from there.
It was the other way round. The 580 is my main card and the 450 is my PhysX card. I've used the 580, single monitor, as the main display card since I bought the computer.
The troubleshooter says it couldn't identify the problem.
Aero
Potential issues that were checked
Mirror drivers don't support Aero effects Issue not present
Aero effects not supported on this Windows edition Issue not present
Video card driver doesn't support Aero effects Issue not present
The Windows Experience Index has not been computed Issue not present
Potential issues that were checked
Mirror drivers don't support Aero effects A running program uses a mirror driver (a type of display driver) which is not compatible with the Aero desktop experience.
The Windows Experience Index has not been computed The Windows Experience Index base score measures the capability of your computer's hardware and software configuration and is one of many factors that determine whether the Aero desktop effects can run. Detection details
Collection information Computer Name: CHRISTIAN-PC Windows Version: 6.1 Architecture: amd64 Time: Monday, August 05, 2013 7:47:54 PM Publisher details
Aero Display Aero effects such as transparency. Package Version: 1.0 Publisher: Microsoft Windows
Aero Display Aero effects such as transparency. Package Version: 1.0 Publisher: Microsoft Corporation
Issue not present Issue not present Issue not present Issue not present
Issue not present
Aero effects not supported on this Windows edition Some Aero features such as transparency are not included on certain Windows editions.
Issue not present
Video card driver doesn't support Aero effects The current video card driver isn't compatible with the Windows Display Driver Model (WDDM).
Issue not present
Issue not present