If it isn't one of the helpful suggestions already made, then you might want to take a look at the Java Run Time Environment (JRE). Have you looked up the proper JRE to use for Oracle 8.1.7? Is that JRE properly installed, and in the class path on your machine?
Since DBA Studio was written in Java it definitely won't work without the JRE. Being that this is Windows you won't have to worry about setting the Display, as windows already knows where the display is.
If you aren't sure what is happening, try launching DBA Studio from dos. You should be able to see the error messages from there.
I have check the JRE.it is of compatible with oracle 8.1.7
if i try to run from dos still same result.i rebooted machine many times but DBA studio does not work.other application like SQL*Plus are working