Thank you for your replies!
Dissapear means the perspectives are still available under window-open pespective-other but there are no icons and the view is a standard view, wich means, e.g. the palette in web development perspective is not there.
There are several error messages in error log view:
eclipse.buildId=unknown
java.version=1.6.0_18
java.vendor=Sun Microsystems Inc.
BootLoader constants: OS=win32, ARCH=x86, WS=win32, NL=de_DE
Framework arguments: -product org.eclipse.epp.package.jee.product
Command-line arguments: -os win32 -ws win32 -arch x86 -product org.eclipse.epp.package.jee.product
Error
Thu May 20 16:04:06 CEST 2010
Unable to find element factory: org.jboss.tools.common.core.resources.XModelObjectEditorInputFactory
Error
Thu May 20 16:04:06 CEST 2010
Unable to create editor ID org.jboss.tools.common.model.ui.editor.EditorPartWrapper: Cannot instantiate input element factory org.jboss.tools.common.core.resources.XModelObjectEditorInputFactory for editor id=org.jboss.tools.common.model.ui.editor.EditorPartWrapper name=web.xml
Warning
Thu May 20 16:33:18 CEST 2010
Perspective JBoss AS has beed made into a local copy
and many more...
This happens also after a clean install (deleting .metadata & .eclipse folders)