Ok, here is how it works:

You put the key in and turn it, the SKREEM sends an RF signal to the little chip in the key fob, the chip sends back a signal to the SKREEM, if the code the chip in the fob sends back is the right code, then the SKREEM sends a start enable to the PTCM. If it does NOT see the right code, the SKREEM lets the starter engage three times, then nothing - this is the universal code for a SKREEM issue. If you disconnect the battery and reconnect it, you get three more tries. NOW if you keep doing this, after several cycles, the SKREEM is said to collapse and lock up - it will NEVER work. So, don't keep trying until you get this fixed. (The shop may have already screwed up here, if they did now know this.)

Anyway,
Each time you start the car, the SKREEM wants to see the secret code coming from the fob that was programmed into the SKREEM. Mercedes and Chrysler kept a record of what code goes with what VIN. When you order the new SKREEM, they encode it with the original code.

What you are describing is caused by:

1) The chip in the key is bad (this almost never happens)
2) The chip in the key is sending a different code (maybe the seller tried moving key blades from fob to fob - in this case , you need a new key coded the same as the new SKREEM - altho as I read your posts, I see that you have a new key, so this should not be an issue).
3) The black ring around the key is a loop antenna that handles the signal to and from the SKREEM and fob. If this ring is not plugged into the SKREEM, you get exactly what you are describing (this happens from time to time when people tear the dash apart.
4) The SKREEM is bad.
5) The SKREEM was accidentally ordered with the wrong code programmed into it, or the KEY was ordered incorrectly. (I don't see this happening, unless someone ordered a key from some flaky source or they ordered the SKREEM from some flaky source - in which case this is NEVER going to work.)