here's what i would do in order of succesion
1)
try cycling the key from all the way off to all the way on a number of times.

2)
try rolling the car a few feet and then cycling the shifter through all the gears and back to park or netral (neutral safety switch).

3)
try banging on the starter with a pipe or hammer etc (stuck solenoid).


was the car fully warmed after say a highway run when it wouldn't start?

__________________
1984 300D Turbo - 231k....totalled 11/30/07 RIP