Starter motor is fine as I replaced the old one which on testing, was working fine

Thanks, I will try that if I don't get any other suggestions

I'm at my wits end trying to find why my '97' auto discovery won't turn over!!! It was working fine, went to fill up with diesel, got back in car and hasn't started since! So, battery is fine and charged, changed starter motor (checked to make sure it was working before fitting it) and still no...