Once, I ran across the issue where a web part is dropped onto a page, and then SharePoint errors out for one reason or the other. I had to use the Web Part Maintenance Page to fix the problem.
However, there is no way to get to this page from any easily available link. Where is SharePoint link to web part maintenance page?
To get to the Web Part Maintenance page, I appended the query string ?contents=1 to the URL in the browser. Say for e.g. SharePoint web part maintenance page URL would be:
Web Part Maintenance Page could be a real saver when faulty web parts crashing SharePoint. Open web part maintenance page and Remove the faulty web part to get the sites back.