-flushing any caching plugins you might be running, as well as server and/or browser caches.
-deactivating ALL plugins (yes, all) temporarily to narrow down the problem. If the problem goes away, re-activate them individually (one-by-one) to find the problematic plugin(s). If you can't get into your admin dashboard, try resetting the plugins folder by FTP or phpMyAdmin. Sometimes, an apparently inactive plugin can still cause problems (because the hooks remain unless plugins completely removed or some plugins stick around in cached files. So by renaming the folder, you break them and force them inactive). If applicible, also remember to deactivate any plugins in the mu-plugins folder. The easiest way is to rename that folder to mu-plugins-old
-If that does not resolve the issue, try manually re-uploading all files and folders EXCEPT the wp-config.php file and the /wp-content/ directory from a fresh download of WordPress. This should replace your core files without changing your content and settings in wp-config.php file and the /wp-content/ directory. Read the Manual Update directions first!