Dunno about ATI settings, but here's the usual advice;
Latest graphics driver
Latest system drivers
Latest DirectX
Perhaps BIOS update
Clean install of the game
Clean install of graphics drivers (uninstall, reboot to safe mode, clean drivers with tool, reboot and reinstal)
You could check inside the case to make sure any additional power cables to the card are connected (modern cards can't draw enough juice from just the slot).
If PSU is modular, check connection to the unit as well.
Same thing is true for CPU; check that cable as well (should be a connector on the motherboard near the socket).
Listing what OS you're using can also help people help you.
