If you've replaced the battery with a known good one and all the electrical systems are working EXCEPT the starter, I'd suspect either the starter has failed, or the solenoid has failed.

If you were cranking with a weak battery, that can be just enough to push a weak starter/relay over the edge.

Once you get the car starting, check to make sure it's charging. With the engine off, your battery should be ~12.8V or so, with the engine running, you should be somewhere close to 14V if the alternator is working properly. Given that the car sat for a long time, it could have just been a failed battery (has happened to my 500SL twice due to sitting).

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]