I wrote a post a while back about how to fix Flash Builder when it wouldn’t start. I found that there were two things to try, one of which usually fixed the problem. The first was to deactivate a product in the creative suite and reactivate it. The other one was to delete the Adobe Flash Builder folder that is usually located in your users directory. If the deactivation and reactivation didn’t fix the problem, deleting the Adobe Flash Builder directory usually will. The frustrating part is that also removes any customization that you’ve made to your workspace which can take time to set up again. So after doing this many times I finally spent more time looking into what the problem was and I found it. Here’s all you need to do to get it to start again and not loose all of the customization. Inside of the Adobe Flash Builder folder navigate to -> .metadata -> .plugins -> org.eclipse.ui.workbench in that folder there is a file called workbench.xml. Edit this file in a text editor and remove any references to files in projects that you know weren’t open the last time that you used Flash Builder. If you don’t remember just remove all references to files. This may mean that you have to re-open some files, but that’s better than having to configure your workbench again. I was able to find which files were open by making a copy of that directory and then deleting it and opening Flash Builder. It recreates the folder and will open and you can usually see what projects are open. Another thing to try is attempt to open Flash Builder and see if it stays up long enough for you to see which projects are open. If you run into this issue I hope this helps.