help! stranded 400E

Tonight while driving my '92 400E (66K), the car ran fine for awhile when all of a sudden I lost a significant amount of acceleration. The oil pressure was fine as were all of the electrics. In fact, while stopped, the oil pressure stayed all the way up. The car hobbled into a parking lot and eventually died. I tried to start it up again several times and it would not start. It tried to start and just would not turn all the way over - even when I gave it gas. So now my car is stuck in Arby's parking lot. Can anyone tell me what is wrong? Any help is appreciated. Jim.