I had the same problem with my car. 1994 e320. I was driving, then all of a sudden the radio had no sound, the locks didn't work, and the seatbelt light was flashing, I think the interior lights came on too. Then I turned the car off, back on, and no problem. It was very sporatic, but took place within a week.
Then I came across not being able to start my car. My mechanic checked around, didn't find anything, but replaced some fuses. I also had my starter and ring gear replaced at that time, due to the fact that my ring gear was bent and making a horrible sound when starting. I haven't had a problem since. Don't know if it is fixed for good, or just in hiding. If you find out more about this, let me know.