it just happend for the first time we thought it was the transmistion but it won go forward or backwards.
wont go forward or backwards on 1999 Ford Taurus
Does your shifter feel loose or can you feel it shifting through PND21 You may get lucky and its just a shift cable, unless you see a red puddle under it. Try checking the fluid lvl
You have a transmission range (TR) sensor that tells the transmission what gear to go in. There is a small chance that is your issue. Other than that, verify your fluid level as ghostima96 says. Lastly, you could have had some kind of internal failure that will require additional diagnosis.
I run into this one a lot. Broken trans pump drive shaft or the splines stripped out of the torque converter. With engine off verify level is about 2 quarts over full, start the engine and recheck trans fluid lvl. If the lvl is still over full by the same amount, its time to pull the transmission.