MyBB Community Forums

Just upgraded from 1.6 to 1.8 and I have the old admincp theme and the search etc isn't working (settings).

check whether all files are uploaded correctly & earlier version files are replaced in admin folder & its sub-folders

is MyBB version displayed correctly on the home page in admin panel ?
if so, run file verification tool available at tools & maintenance section of admin panel to find missing / changed files.
ignore files reported from install folder & its subfolders. you have to replace reported files from MyBB source files
pack of your forum's version.

I just downloaded a new copy of admin/styles and just overwrote all the others. Now I'm good.