Eclipse will not start and I haven't changed anything

I used eclipse -clean -clearPersistedState and that worked for me. You will lose your window layout configuration, but that seems minor to me.

For Linux systems try: ./eclipse -clean -clearPersistedState

See Eclipse JUNO doesn't start

Ok so i figured it out. Go to yourWorkspace/.metadata/.plugins and delete everything in there. Eclipse will start and repopulate the folder.

Removing workbench.xmi under workspace/.metadata/.plugins/org.eclipse.e4.workbench/ worked for me. It did not remove the existing projects.