Had my headlight changed by my ex, now the car wouldn't start. Took the battery in and replaced it. Got the battery put in. Now it cranks but doesn't start. Hoping it something simple like my alarm won't allow it!
I had similar symptoms on an old ML320. It turned out the be the camshaft position sensor. Probably coincidental that it happened when you changed the battery, but an electrical trauma like arcing when the battery was connected could send enough transients into the electrical system to end the life of a near gone CPS.
Does "cranks but won't turn over" mean the engine does turn over but never actually starts? I don't know about this particular model, but it's possible there's some kind of anti-theft setting that needs to be re-set. Perhaps your owners' manual discusses the anti-theft system, or you could call a local dealer or Mercedes specialist. Or, search the internet.