Cranks but will not start
 

1999 SLK 230, 65K miles, driven infrequently, maybe sits for a week or so without being driven. Now it will crank but does not start. Charged up the battery. I suspect no fuel. Does someone have the troubleshooting process for this? I have searched but there is not much written up on this problem. Any help would be great, also links to DIY aids with potots are my speed. I have tools and can do the work, just would like to know things like where is the fuel filter, and on the fuel rail there is a brass cap fitting (what is the for?).

Thank you in advance.

Neil

mercedesml 320 stalling