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If your car is cranking over fast enough it could be
your fuel primer may be leaking and letting air into the fuel system.
Try pumping your primer and if fuel is leaking out then that is your problem.
I had the same thing happen to my 83 300D ,but being cheap at the time I just pumped the crap out of the primer to get the fuel system filled again regardless of the fuel leaking all over my hand.
Got the car to start.
After that I started the car everyday until I got a new primer pump.
Of course it could be the fuel pump, but I 'd try the primer first.

If it won't crank, then it is electrical and the advice above should be looked into.

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