I am having this same issue and I am unable to resolve based on the above thread.
Using v2.3.1 - Build: date 20111017
Last week the CP was working fine. Suddenly this week none of the main nav links (content, design, members, add-ons, admin, tools) work, nor any javascript-dependent elements. I can’t think of anything that could have changed to cause it.
I have verified the path settings and that javascript is enabled in my browser.
I have cleared my browser cache and the EE cache folder.
I have re-uploaded the entire Themes directory from the EE 2.3.1 install package after first deleting those files on the server.
Can someone please help me ASAP?
Thanks,
-m