If the AT light comes on then this means you have a malfunction with in the transmission control system ,
Could be anything from a output speed sensor to the operation of the valve body and solenoids.
You will have to get hooked up to a scan tool in transmission mode to get the malfunction codes .
Not much you can do .beside disconnect the battery for ten minutes to clear codes and reset the transmission then try and drive ,
if the car now drives then you have a sensor issue ,if still no drive then you may have a internal failure .
If you do have drive then you need to get to your local dealer or transmission shop and have the transmission diagnosed .
Need any follow up help then please get back to me with the reply button, and not the poor or bad service.
This way i can get back to you or suggest another expert if needed.
If i do not get back to you then i may be off line, and when i get back online i will get back to you..
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Kind regards Greg.