Try pulling out fuse #28 for a few minutes, then re-installing it, and see if COMAND starts working normally again. It's located in the fuse box at the left side of the dashboard. There's a cover that pops out to gain access. It's only visible with the drivers' door open.

If it doesn't work, go to the fuse box in the trunk. It's behind the access door on the left side. Remove and re-install fuses #3 and #6. This wil re-set the NAVI drive unit and the Audio Gateway.

Of course, make sure the fuses aren't blown when you remove them.

If it still doesn't work, let us know how you like the free coffee in your MB dealers' waiting room.