Answered by Sayyidi Habib Umar bin Hafiz (may Allah protect him and benefit us by him)
I have not cried for a long time, not even in dua. What should I do?
You have to have remorse for not crying from awe or yearning for Allah. This regret is the first step. If this regret is true and strong then other steps will follow, like trying to make yourself cry. This should be followed by reflecting upon the sayings of Allah and His Messenger, and the sayings of those who had fear of Allah. All of these things are causes by which Allah will return softness to the heart and return submission to Him.