With so little information I doubt anyone will be able to help you.
you need to do two things:
a) turn off the 'error.htm' setting in the web.xml file so that you get the full stack trace of what's going wrong when you load the page. You could also find out what's going wrong by looking at the log file.
b) did you add the jena.jar to the WEB-INF/lib directory of the application, or put it under the jboss/server/default/lib directory?
c) check out the jena users list at http://groups.yahoo.com/group/jena-dev/