my command unit turns on, the mercedez benz logo comes on and then I guess it turns off, since nothing works, no radio, no naviagation, nothing works. I have a 2008 E-550. I really hope someone can help me.

i had the same thing happen to me in my '05 e55. if the '08 E550 is based on the fiberoptic system, "MOST", commonly referred to as, then there is something in the "ring" thats not working. could be the cd changer, nav or voice command system, the sirius sat system, etc.... whenever a component thats part of the ring is not working, the communication between all the components are interupted and thats why the system just turns off when you first try to turn it on..... unless you have a STAR system, you will need to take it into the dealership and they will be able to tell you which component is failing to "return" the signal back to the main unit. on my car, it was the sat radio that i wasnt even using that died and since i wasnt even using it, i spent much time and money buying components to replace each component until finally i gave up and let the dealership figure it out after $700 later. once the component is repaired or replaced in working order, the "ring" will be complete again and everything will turn back on like usual. the "ring" are the various components that make up your entertainment system, whatever it is you have, and when you first turn your system on, a signal is sent to each component and continues around the "ring" until it returns back to the comand to report all is in working order and then it turns on.... this is done very quickly btw. sorry for being so long here, but i hope it helps.

Thanks alot. I was already thinking about having to buy a command center. I will take it to the dealer and see what they tell me, and take it from there. Thank you

Let me know if you need any of those parts. I have a couple of W211s to pick from