Custom Resolution Problem ! Please Help !!

[TuanProGTA]

Ok, I've been using this system spec:
-Intel Core i7-2600K
-Asus GTX580
-Windows 7 Ultimate Build 7600
-Samsung E1720NRX 17" LCD Monitor
In Nvidia Control Panel, I create 3 custom resolution :
- (1920x1536 Aspect ratio 5:4 )
- (2048x1536 Aspect ratio 5:3 )
- (2560x2048 Aspect ratio 5:4 )
All 3 custom resolution working just fine when I set Destop Resolution and Ingame Resolution, with the old GTX580 my monitor can handle max resolution 2560x2048.
But, when I update my hardware to :
-Intel Core i7-4770K
-Asus GTX780
-Windows 7 Ultimate Build 7601
-Still using Samsung E1720NRX 17" LCD Monitor
I have the problem with Custom Resolution in Nvidia Control Panel, I can only set the resolution up to (1920x1536 Aspect ratio 5:4 ) when I try (2560x2048 Aspect ratio 5:4 ) pressing the Test button, my monitor just appear flashing black screen and when back normal, not have a bulletin board tell me that resolution not available on my monitor ( the weird thing is with old GTX 580 I can set this custom resolution )

Any suggestion ? Please help me, thanks everybody in advance !

[ToastyX]

The E1720NRX is a 1280x1024 monitor. I don't know how you got it working before or what settings you used. 2560x2048 is a high resolution that requires a lot of bandwidth.

If you were sending the resolution to the monitor and the monitor was downscaling, then you need to use the "CVT reduced blank" timing standard to fit 2560x2048 within the VGA pixel clock limit.

If the GPU was downscaling, then you need to enable GPU scaling and use the timing parameters for 1280x1024 while setting the display mode to the higher resolution.

[TuanProGTA]

Thanks you so much for reply my question !
With my old GTX580, I just go to Nvidia Control Panel and set the custom resolution to 2560x2048 and everything just fine, with the Timing is Automatic.
Yeah I know it's a 1280x1024 monitor, the point that I'm try to making the custom resolution is I wanna downsampling 2560x2048 to my actual 1280x1024.
Can you please explain more detail those two suggestions ? ( sorry for my bad English )

[ToastyX]

Did you try the "CVT reduced blank" timing standard instead of the "Automatic" option?

[TuanProGTA]

Of course I try "CVT reduced blank", and I'm also try all the timing option too but with no luck, it's really driving me insane

[ToastyX]

First, make sure GPU scaling is enabled. Then set your resolution to 1280x1024. Then add a custom resolution but switch to manual. The active pixels should say 1280x1024. Change the resolution at the top only. See if that makes the GPU scale the resolution.

[TuanProGTA]

Ok, still nothing happen
But I find something in "Adjust desktop size and position", in Scaling tab, when I tick to "Full-screen" box and chose "Perform scaling from", of course GPU is chosen. Then I can add one more custom resolution 2048x1536.
But when I tick to "Aspect ratio" box, delete the 2048x1536 resolution and try to add it again, the black screen come back and nothing happen !

- EDIT -
Ok, my monitor only have the VGA port so I must use a "DVI to VGA" adapter to connect. Try playing around with different adapter type and finally I can set the Custom Resolution to 2560x2048. BUT the resolution not fit to my monitor, the width is fit, but the height is stretch down the bottom of screen.
Any suggestions ?