A couple of days ago I replaced my Nvidia GTX 275 with a GTX 560 Ti, which worked with no problems. The monitor I'm using is a Viewsonic VA1916w and it's connected through a DVI-VGA adapter. Its native resolution is 1440x900.
Then I tried updating its driver from version 280.26 to 285.62, and as soon as the installation finished, my resolution changed to 1024x768. When I tried to change it back, the list didn't include the correct resolution and the name of the monitor had changed to 'Generic Non-PnP Monitor'. The system has assumed that the native resolution is 1024x768.
I've tried uninstalling and reinstalling the drivers (both versions), replacing all of the cables and the DVI-VGA adapter, creating a 'custom resolution' at 1440x900 (it was really blurry because it had to be scaled twice), and making sure all the cables are fitted well. The problem goes away completely sometimes, but then it always comes back when I restart the computer.
Right now I'm using 1280x960 (since that's closest to the native aspect ratio - 1280x800 gives a 'out of range' error on the monitor) and I'd really appreciate some help :)