Hyundai Q90U Resolution Problems Garbled Screen

Hi, i'm having some problems with my new monitor.

I'm using GeForce 6800 GS with the above monitor when i play Sid Meier's Pirates or Need For Speed Most Wanted i can only play in 640x480. Other resolutions are available but when i select them the display becomes garbled with lines across it. When i press print screen to get a screen shot it turns out ok in MSPaint so presumably it's a problem with the monitor and not the video card.

Any help/suggestions accepted

Chris