Dear List, 

After a few changes i have here an example: 

It works, but what I wanted to know is why are there  

round brackets after writing \starttheroem if i compile it. 

Should be without round brackets. 

I have the following example, the text was in a PDF from 2008, called: Theorems in ConTeXt, and also my text with the margin:

\definemargindata  [MyInMargin][inright]

\definemarginframed[MyInMargin][topframe=on,bottomframe=on,rulethickness=1pt,width=1cm]

\margintext{\blackrule[color=black, height=0.25ex, width=1cm]\\}\blackrule[color=black, height=0.25ex, width=7cm]

\setupenumerations

  [ before={\blank[big]},

    after={\blank[big]},

    location=serried,

    width=broad,

    distance=0.5em,

    headstyle=bold,

    titlestyle=normal,

    way=bytext,

    conversion=numbers]

\defineenumeration

  [theorem]

  [    text=Theorem,

      title=yes,

      style=italic,

       list=all,

   listtext={Theorem }]

\starttext

\margintext{2.1.1}{\starttheorem {The square on the hypotenuse is equal

to the sum of the squares on the other two sides. Ach is das schön, dass du da bist}

\stoptheorem

\stoptext