I drive a 1983 240D.

Last night, I was sitting at a stoplight in Second gear. The light turned green and I shifted to Drive and gave it some gas. I immediately heard a clunk (nothing extremely loud), and although my shifter was in the Drive slot, it felt like I was still in Neutral. I shifted through all of my gears from Park all the way down to Low with the same result. My engine currently runs great, the car will just not get into gear. Can anyone give me their opinion on what might be the problem? Is it the transmission? Driveline? Linkage? Thanks.