Today I had a similar problem to the one in this post – but instead of hanging, Flash Builder just failed to start up and quit during the “loading workbench” phase of initialization.

In the earlier post, I mentioned deleting a .snap file in [workspacelocation]/.metadata/.plugins/org.eclipse.core.resources, but previously I hadn’t been able to find it. This time, there WAS a .snap file in that folder, but it was hidden.

Deleted it, and Flash Builder starts up like a champ.