How to get my Nikon SB-900 to work with my Nikon D3S to shoot at 1/250th of a second?

All my efforts only get the flash to work at 1/60th of a second. Please tell me what settings to use so I can get this to work at 1/250th of a second.

The D3s syncs at 1/250th second or less

Look on page 113 of the user manual.

My guess is that you are not using the camera in the manual mode or using shutter priority. Do that and see if you can shoot at 1/250th second