[plt-scheme] help regarding stepper

I have  installed Dr Scheme version 301 English .Whenever after
writing all the  lisp definitions and successfully running  the
program I click on step button it opens a new window dissplaying "all
the definitions have been successfully evaluated . But it never
displays the step by step evaluation in the new window .When I click
on step button nothing happens . I am expecting a line by line
evaluation of program with some facility of watch variables so that I
can successfully debug my program.Do help.
-- 
amol aggarwal