Q:

unable to open Eclipse Juno IDE

I have just installed Jboss tools (Juno) plugin in Eclipse Juno, after i installed i restarted for getting the changes but from that time onwards it is not opening the IDE. It has stored the following error in log files.
java.lang.RuntimeException: Application "org.eclipse.ui.ide.workbench" could not be found in the registry. The applications available are: org.eclipse.ant.core.antRunner, org.eclipse.datatools.connectivity.console.profile.StorageFileEditor, org.eclipse.e4.ui.workbench.swt.E4Application, org.eclipse.e4.ui.workbench.swt.GenTopic, org.eclipse.equinox.app.error, org.eclipse.equinox.p2.director, org.eclipse.equinox.p2.garbagecollector.application, org.eclipse.equinox.p2.publisher.InstallPublisher, org.eclipse.equinox.p2.publisher.EclipseGenerator, org.eclipse.equinox.p2.publisher.ProductPublisher, org.eclipse.equinox.p2.publisher.FeaturesAndBundlesPublisher, org.eclipse.equinox.p2.reconciler.application, org.eclipse.equinox.p2.repository.repo2runnable, org.eclipse.equinox.p2.repository.metadataverifier, org.eclipse.equinox.p2.artifact.repository.mirrorApplication, org.eclipse.equinox.p2.metadata.repository.mirrorApplication, org.eclipse.equinox.p2.updatesite.UpdateSitePublisher, org.eclipse.equinox.p2.publisher.UpdateSitePublisher, org.eclipse.equinox.p2.publisher.CategoryPublisher, org.eclipse.help.base.infocenterApplication, org.eclipse.help.base.helpApplication, org.eclipse.help.base.indexTool, org.eclipse.jdt.apt.core.aptBuild, org.eclipse.pde.junit.runtime.uitestapplication, org.eclipse.pde.junit.runtime.legacytestapplication, org.eclipse.pde.junit.runtime.coretestapplication, org.eclipse.pde.junit.runtime.coretestapplicationnonmain, org.eclipse.pde.junit.runtime.nonuithreadtestapplication, org.eclipse.wst.server.preview.preview, org.eclipse.ant.ui.antRunner, org.eclipse.emf.codegen.CodeGen, org.eclipse.emf.codegen.JMerger, org.eclipse.emf.codegen.ecore.Generator, org.eclipse.emf.importer.ecore.Ecore2GenModel, org.eclipse.emf.importer.java.Java2GenModel, org.eclipse.emf.importer.rose.Rose2GenModel, org.eclipse.jdt.core.JavaCodeFormatter, org.eclipse.jdt.core.JavaIndexer, org.eclipse.pde.build.Build, org.eclipse.wst.jsdt.core.JavaCodeFormatter, org.jboss.tools.vpe.browsersim.eclipse.application.
    at org.eclipse.equinox.internal.app.EclipseAppContainer.startDefaultApp(EclipseAppContainer.java:248)
    at org.eclipse.equinox.internal.app.MainApplicationLauncher.run(MainApplicationLauncher.java:29)
    at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:110)
    at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:79)
    at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:353)
    at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:180)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:629)
    at org.eclipse.equinox.launcher.Main.basicRun(Main.java:584)
    at org.eclipse.equinox.launcher.Main.run(Main.java:1438)

please help me out.

A:

Eclipse applications are provided in plugins. The "org.eclipse.ui.ide.workbench" application is the entry point of the Eclipse IDE, it's comparable to the main-method in java or C programs. 
The Eclipse IDE has it's application, the main program entry point, in the plugin "org.eclipse.ui.ide.application". This plugin declares the IDE application in the plugin xml:
<extension id="org.eclipse.ui.ide.workbench" point="org.eclipse.core.runtime.applications">
    <application>
        <run class="org.eclipse.ui.internal.ide.application.IDEApplication"></run>
    </application>
</extension>

Your messages reports that this application could not be found. 
There are many possible reasons. Eclipse plugins declare dependencies and Eclipse is a big graph of dependent plugins. An invalid plugin results in other plugins, which require this particular invalid plugin, getting invalid too. This is most likely what happened to you. For some reason your install behaved wrong and removed, killed or invalidated your plugin graph in some odd way. The Eclipse application therefore wasn't  exposed and thus Eclipse refused to start.
Fixing this is usually very tedious, you would have to find out which plugin was trashed and corrupted the whole IDE. Far more easy is to simply use a fresh install (use a fresh download and install your plugins on top).

