please help - sync speed, wrong settings, just stupid??....

Stop.

Take a deep breath.

Use full manual mode. Always.

Set the shutter speed to 1/250th and aperture to f11 and ISO200. Shoot. Make sure the strobe is firing. you should see a black bar because the max sync speed of the D90 is 1/200th.

Now lower the shutter speed to 1/200 and repeat. If still black bars then lower the shutter speed one click at a time until they go away.

Kent