my 1994 mercedes benz keep cutting off i cranked it but it keep cutting off i have changed the crank shaft, crank sensor, and computer. what could the problem be?

we have to check the basics here...air, fuel, spark, timing...and valve timing~ can you hear the fuel rushing through the fuel rail when you turn the key to the ON position? If you pulled a sparkplug wire off and put a phillips screwdriver in that, could you hold it close to ground to see the spark? have someone turn the key for you to see if we've got spark..the valve timing concerns me...a chain easily stretches to where it jumps a tooth...still runs like poop, but will still run if this might be the case here...you could take the timing cover off to inspect the position and wear of the sprockets, chain tensioner and wear shoe...if a timing BELT engine CHANGE it for it's age purposes only~

Your starter solinoid or your ignition switch is bad. I would bet on the starter soliniod

Or the starter solinoid relay

Do you mean that it will run as long as you are turning it over than it will not run?