A couple of times now I’ve done something a little boneheaded that causes a notebook to become unresponsive. Since the notebooks are always evaluated when they’re opened, there doesn’t seem to be a way to recover the notebook: every time I open the notebook to delete the offending cell, it hangs. It seems like I have no other choice but to delete the notebook and start over, is that right?
There’s a (as-yet-undocumented) “safe” mode you can use to recover your notebook. Just add “/safe” to the URL. Your edits there will be saved as normal, but none of the code is evaluated.