This is what's known as a "hard re-set". It's a great way to restore functionality to all kinds of mis-behaving automotive electronics. I use this technique regularly to bring dead ECU's back to life, in fact, I did this about an hour ago to revive a W204 instrument cluster. The re-set is a diagnostic tool though, not a fix.

The COMAND system on your car is the first version COMAND for the W211. There are plenty of known issues, many of which can be fixed by installing updated software. Most likely will require a trip to the dealer. Having the system scanned for fault codes should be your first step.