1993 300E will not start

[Early Bird]

Ok you Tech Wizrads out there, maybe you can help with Info only. At lunch time today, a person picked me, out of hundreds to help start his 300E. The lights worked good, the radio worked but when you turn the key you get nothing. No starter, no clicking noise, nothing. I know there is numerous things that could be causing this type of problem. What are they?? I would like to be prepared when this happens to me. This Gentleman just stopped for a short period of time, and than returned to his MB to end up STUCK. I gave up and was watching at a distance. He called a Tow truck for help. When he showed up the first thing he did was try to jump start the MB. Nothing again, not a click, clank or spit. This is all the information I have on that MB. Lets hear your thoughts, please !!!!!