One day after i migrated a Drupal 7 website to a client’s server, the core drag and drop feature did not work. In addition, i could not edit the Context because nothing was shown when i select the condition. The Show row weights link was also missing.

Finally i found that i was not the only one who came across this problem. The following post is a similar scenario and probably the failure was caused by the PHP 5.3 on the client’s server.
Drupal Core – Drag and drop not working
 

Anyway, after i have enabled the Aggregate JavaScript files in Administration » Configuration » Development » Performance, the problem was gone.

Done =)