transmission problem

I am new to this site. I drive a E320 and my son has been driving a 98 ml320. A few weeks ago he started to lose power as he was driving and the speed would decrease. Dealership replaced a sensor but shifting problems continued. This week, he felt like he had hit a bump. As he slowed he heard a grinding noise, like if your brakes pads were totally worn. He slowed the car and stopped. When he started it again, it would not move. Does he need to replace his transmission?