2003 Audi A4 Questions

I have had problems with my torque converter slipping constantly especially when the car is speeding up to 45mph. I went to an audi dealership and they told me I need my torque converter replaced. Today I was driving on the highway and my car stopped responding to gear shifts and pressing the gas. The car is still able to reverse however when I put it into drive and hit the gas, the rpm's go up, the engine roars, the car doesn't move. I put the car in nuetral and I can roll it, if I put it in park it doesn't roll. What can be the problem?

Audi A4 3.0 quattro 2003, automatic tranny.