[EDIT: PROBLEM RESOLVED, SEE POST #7]
Back in mid-May, a girl ran a red light and clipped the front corner of my 2005 S500 4MATIC. There was damage to the fender, bumper, turn signal, headlight, and windshield washer tubing.
I drove the car home after the accident, filed an insurance claim, and drove the car to a body shop. Insurance totaled the car as estimates climbed north of $7000, as finding new parts on a 17-year-old Mercedes is expensive. I have a lot of money in this car with all new Airmatic struts, Mercedes valve body, compressor, upper and lower control arms, axles, GROM Bluetooth and USB and Aux audio upgrade, newly refinished wheels and new tires. Insurance allowed me to keep the car and salvage title it for about $1000 (that is, the payout for totaling the car was reduced by about $1000), and I decided to do that and have the car repaired. The body shop I had the car at has a policy that they do not work on salvage title cars at all, so I had it flatbedded to another shop.

The new shop contacted me and said the key doesn't turn, and all the electric is dead, and the battery won't hold a charge. The battery was a fairly new correct AGM battery directly from Mercedes, so I got it replaced under warranty and dropped off the new battery. They contacted me again and here's the current problem:
-The key will not turn. The car doesn't respond to anything on the key. None of the buttons produce any response from the car. No door lock/unlock, trunk open/close, start, etc. But the electric from buttons in the car works, such as door locks. They tried replacing the battery in the key fob in case that was the problem, and that didn't help. I brought them my second key fob and it's the same issue. No response from the car to the key, and key won't turn. They said it's weird that the steering column is NOT locked. They said they think it might be in a theft-deterrent mode, or they guess that perhaps a critter got into it and ate wiring while it sat a few months.

I'm skeptical that a critter got to it, and they said there was a note from the first body shop on the key saying that the car won't start, which is bizarre since I literally drove the car to that body shop after driving it home from the accident.

My questions: Does anyone have any suggestions for obvious things to check? We can only speculate what the first body shop did; perhaps they tried to jump-start it and fried something etc. I'm just looking for suggestions from anyone with any experience with this type of problem. We have the parts needed to rebuild my car, but this issue may push my to part out the car if we can't get past this. Electrical diagnostics can go sky high, so I'm trying to narrow down what to check. All ideas welcome.

 

You might try unplugging or removing the alarm system, located behind the left-front fender-well lining.

 

Thanks, I'll pass that along. It's behaving as if the key fobs are not synchronized to the car, but I've read that the key is designed to not turn if the steering column is NOT locked, and that is the situation, and I'm not finding a common solution for this problem. I do find online a number of people who have this problem when their battery has been disconnected for a period of time, so there seems to be a common related cause but no specific solution.

 

Is there steering locking on your model year? On the 2000's there is no steering lock.

Try to have the key in the EIS for a couple of minutes (10 to 30), sometimes it might need to sync itself that way.

Do you have keyless entry?

 

The W220 cars do not have a mechanical steering lock. The battery in the key fob has no impact on whether or not the key will turn in the ignition - that power is furnished to the key fob thru inductive coils.

 

My S500 4Matic does not have keyless entry.

 

Problem resolved!
Fuse #78 in the passenger dash side was blown. Apparently in addition to driving the EIS module, it also powers the alarm.
The fuse blew immediately after replacing, and disconnecting the alarm horn causes the fuse to not blow, and allows the car to start and run and do all the things that it is supposed to do.



Speculation is that when the car was moved from Body Shop #1 to Body Shop #2 the alarm may have gone off, maybe overheated and shorted or otherwise failed in some interesting way; but who knows? The battery had failed and wouldn't even take a charge by the time Body Shop #2 got working on the car, so . . .the things that restored function:
1: New Mercedes AGM battery
2: Replace fuse #78, discovered there is a short in that circuit, isolated short to alarm system, disconnected alarm system, and replaced fuse #78 again.

In case this helps anyone else. Thanks for the tips and advice here, especially user WallyP.

 

The alarm unit contains lithium batteries, and one of the most common failure modes is failure of those batteries, with subsequent corrosion.

I would not bother to install a new alarm...