I had this issue on version 3.5.1. After reinstalling several times, clearing my cache, history, cookies, DNS cache, etc etc to no avail, I went into the server side of things to see if I could figure it out there.
I found that I could modify the WP tables in the database to unfold/un-collapse the admin menu. I modified the wp_usermeta table. I changed “wp_user-settings” from “mfold=f” to “mfold=t” and that seemed to solve the problem.
This was so frustrating! Hopefully that helps some of you!
