|Which specific Gateway model is it ?|
That's probably on a label on the outside of the case.
You could try the monitor with another working computer, but there's probably nothing wrong with it.
In most cases there is no setting in the bios that actually disables the onboard video - the onboard video is disabled automatically when there is a video card installed in an AGP or PCI-E X16 slot.
(The only exception to that, that I know of, is when the mboard has onboard video and the main chipset is a recent one that supports Hybrid video - both the onboard video and the video on a card in a PCI-E X16 slot working at the same time.)
It's NOT disabled automatically in any case when there's video card in a PCI slot.
"It did say "Your video card has stopped working" when i had it set to my 460"
Some times a video chipset is damaged such that it works in basic VGA mode, which is what it's using while booting before Windows loads, or in Safe mode, or in Enable VGA mode, but it doesn't work in Windows when you load Windows normally and the specific drivers have been loaded in Windows for the video adapter, or visa versa.
Remove the AC power to the computer.
Unplug the 460 video card.
Plug the monitor into the onboard video port.
Restore AC power and try booting the computer.
If nothing else is wrong, you should have video while booting before Windows starts to load, and after it starts to load in Windows.
If you DO have video every time before Windows starts to load, but no video in Windows. with the onboard video...
For 2000 or XP...
See response 9 here:
Boot into Enable VGA mode.
Note - that's missing this...
Remove any bootable CDs or DVDs you have in drives.
Press F8 repeatedly while booting, don't hold down the key, starting very early in the boot.
When the Windows "Advanced..." menu appears, choose Enable VGA mode.
For Vista, or Windows 7....
See response 1: