6800GT Video stuttering

I have a 6800GT which im running in my main windows XP Pro system, recently divx/avi/mpeg video played with either VLC or windows media player. However, if I open dxdiag and turn off directdraw it functions normally.

I've updated directx, reinstalled windows, tried numerous nvidia drivers and have also tried 4x AGP and fast writes off. Im worried that the card may be on the way out so would welcome any suggestions you guys may have.

I've also run memtest and had no error's.