I have a 2009 CLK550 and it won't turn over. I went into the store and when I came back out, it wouldn't turn over. Everything still had power, the windows, sunroof, radio, headlights, ect. I tried jumping it off, but no go. A friend of mine suggested a hard reset, so I disconnected the battery cables, waited a couple of minutes and reconnected. With the key fob, I locked and unlocked the doors, got inside, closed the door and it still won't start.
in the process of doing this, I noticed the front intake valve was disconnected. This explains why the engine was bogging down while it was idling.
Could this be the cause of it not starting now?
Any help or suggestions would be greatly appreciated!

Sounds like it could be a crank position sensor and/or a fuel pump related issue. Any check engine light?

I'm sure by now you've gotten a tow but I would see if you can get a scanner on it and see if its throwing any codes.

Also, it may not be a bad idea to go to auto zone and buy a test light. They're super simple to use. Go through all of your fuse boxes (under the hood, Trunk) and check all of your fuses to make sure noting has shorted out. It's possible you're not getting fuel pressure due to a blow fuse. Do you hear the fuel pump kick on when you turn the key?

I would start there and see if anything comes back.

- Joe

OP.... Please define "Won't turn over."

Does this mean 'You ask it to crank and it does not crank on the starter?'

Or does it crank on the starter but not start?

If the starter is cranking the engine first suspect is a crank position sensor. You *should have one in the glovebox with tools to replace it as they are a common enough failure.

It's not cranking at all. There's absolutely nothing when i turn the key.

I will check that and get back to you

How old is your battery?