IntelliJ Code Completion not working for new Java classes

Question

IntelliJ IDEA 13 has started exhibiting a very weird behavior in my local setup.

Namely, in any new Java class added to an existing project

Answer 1

There could be 2 reasons for your problem

1. Either the the source folder is not properly configured in the your build java build path. If the source folder is not properly configured the autocomplete wont get the required class definitions and autocomplete would fail for your project.
2. Restoring the default options in 'Windows > Preferences > Java > Editor > Content Assist > Advanced'