This happened on my 02 CLK cabriolet memory seats. There is a fuse box in the boot under the carpet. Have you looked there? Sorry can't remember the fuse numbers but there's only a few and you can check them all.
Have you checked all the connections under the seat?
The other thing is check the fusein the front, takie it out and 'spark it' dab it in and out with the ignition on, then turn the car off and come back to it. This happens with mine and it kind of resets it.