2005 Ford Taurus - Trans issue

This car was given to me by my bro-in-law 1 1/2 years ago and I have driven it since then trouble free. He bought it new and says it has been a good car for him. Now suddenly, without prior symptoms, I have lost all transmission functions. when shifted to drive, 2nd, or 1st gears, it will not move. Is there anything, other than a shot transmission, which could possibly cause this? Thanks, Jim

Low fluid.