Try to tail -f the server.log in $jbpm_installer/$jboss/server/default/logs to see what errors you are actually getting so there is guessing going on.
*web editor shown, however no diagram appears -> what oryx designer version are you using? There is an information button in the toolbar which should give you the version. Both of the evaluation processes open without issues with designer-1.0.0.053 and should also with designer-1.0.0.052
*designer blocked forever in "loading assets". -> parsing error when opening the bpmn2 of your process, again server log should show you what happened
*try running "ant stop.demo": no way, got stuck in "stop.jboss" -> whats stuck mean? Looking at server and boot logs will allow you not to have to guess
*the last option: reboot - seriously? :)
Please prodive more info. Thanks.