vga display issues

[IAmNoon1995]

So I have got a 800x600 pixel display working but when I try to get the vga to display at 1280x800 pixels io get the error it says "video mode was not detected (line len = 1681, h Sync len = 136, hNegitive=false, line count = 829,v Sync len = 3, vNegative=false" I do not know what to do I have tried to fix it but it has not worked can i get some help with this.

[hneemann]

Each video mode uses different timings for h-sync and v-sync and the sync polarity also differs. This is how the monitor recognizes the video modes. It is not sufficient to simply output a different number of pixels.

The video modes that are supported and the corresponding timing parameters can be found here.

The mode 1280x800 is supported.

[IAmNoon1995]

here is what I have been trying to use (new VideoMode(60, 83.46, 1280, 64, 136, 200, 800, 1, 3, 24, true, false)); this is the one that I trying to use but I get that error I do not know how to fix I have it set up similar to my display using this display (new VideoMode(60, 40, 800, 40, 128, 88, 600, 1, 4, 23, false, false).

[IAmNoon1995]

This is the non working 1280x800 display.

This is the working 800*600 display.
I just did this on my phone I do not know how it will look if it turns out bad sorry.