Mario, one click usually signifies a bad starter, connections at the starter, or a bad battery connection. Also check ground W16 at firewall.
http://www.benzworld.org/forums/w163-m-class/1632789-99-ml430-144k-all-sudden-wont.html
http://www.benzworld.org/forums/w163-m-class/1632789-99-ml430-144k-all-sudden-wont.html