Mercedes 300E transmission question

I have a 1989 300E Mercedes. When motor is started, there is a "whining" noise but the noise stops when I put it in forward gear. When I put the car in gear, it won't move forward. The transmission fluid level is full and does not have a "burned" smell, the fuild appears good. It will go, somewhat, in reverse but barely moves forward. Do you think the transmission is bad or do you think it could be something else, especially with the "whining" noise. please advise & thanks in advance.