Have you tried:
– deactivating all plugins to see if this resolves the problem? If this works, re-activate the plugins one by one until you find the problematic plugin(s).
– resetting the plugins folder by FTP or phpMyAdmin? Sometimes, an apparently inactive plugin can still cause problems.
– reviewing http://ww.wp.xz.cn/support/topic/411649
Well you’re right; it’s definitely a plugin problem because I’ve disabled all of them and the menu was restored. I guess I’m going to find out the culprit soon. Thanks.
V.
I had a similar problem and Social Discussions seemed to be the culprit.