Normally when this happens it's one of a few things. You have a bad video cable. You have bad drivers. You have a bad video card/mobo. You have software installed controlling the colors such as ATi's Catalyst Control Center. Seeing as you set the monitor to default and it remains discolored when it's not even connected, it's probably a bad monitor. Your video controller card(VCC) is probably bad and would have to be replaced. If it's recently bought, try to return/exchange it. If it's not under warranty try hitting it really hard on the side and seeing if it flickers and starts working. If none of that works, new monitor? I doubt yours has the option, but a select few monitors have serial ports or even usb ports that allow firmware flashing. If it did, you could check into seeing if you could flash a newer firmware? Normally it's a problem with circuitry however and not software.