Windows 7: Resolution problem with BENQ EW2420?

I bought the BENQ EW2420 monitor and I have a problem when using the standard VGA driver.
The screen is 1920x1080 but as I change GPU drivers, the screen will load the standard VGA driver and will not allow me to select more that 1024x768 display.
The display then has huge black borders around the edge, why does it do this?
Thanks.

You need to install the drivers for your evga gtx295!! Go to nvidia for those: NVIDIA DRIVERS 275.33 WHQL

Sorry but I already have the latest drivers but what concerns me is why the standard VGA driver only displays up to 1024x768 ?
And why does my monitor show huge black borders around the edge?
My previous samsung 1920x1200 monitor didn't do that.
Does the benq ew2420 not have an internal scaler?
Thanks.

If standard display drivers are showing in device manager then you have no drivers installed!! It should show your gfx card in the display adapters. Like in the image below:

Thanks Anthony but it does show the correct drivers but what I mean by my explanation is when the drivers are uninstalled and windows install the standard vga driver.
Sorry for my terrible explanation.

Its the nvidia card that supports the screen resolution. Without the drivers it cant process large screen resolutions.

Hope that makes sense.

Thanks Anthony, that makes sense.
I just can't understand why my older samsung 1920x1200 would fill the screen and this benq 1920x1080 doesn't.