1) Make sure to read this post for plugins and themes known to have issues with 4.0 (down at the bottom): http://wordpress.org/support/topic/wordpress-40-master-list
2) Sometimes the update is not quite completed successfully. Doing a manual update (upload the latest WordPress files to your server, overwriting the old ones – with the exception of wp-config.php and the “wp-content” folder) often fixes this issue.
3) And finally, doing basic troubleshooting to identify the most likely reason for the issue. To do this, disable all plugins and any custom themes. Then test your site. If everything works, great. We can rule out WordPress and your server environment as being the source of the issue. Now enable your custom theme and test your site. Does everything work? If not then we know the issue is probably with the theme. Contact the theme developer for support. If it does work, great. We now know the theme is not the issue. Now start enabling plugins one by one, testing after you enable a plugin. If the issue shows up, note which was the last plugin you enabled and contact that plugin developer for support. In this way you can help narrow down and possibly even identify the reason for the issues you’re experiencing.
4) Make sure to update all your plugins! Some old versions of plugins don’t work with the new WordPress update.
Thanks a lot.
The issues are solved after I disabled a plugin called Comprehensive Google Map Plugin. When I deactivate and re-activate the plugin, it says the plugin is not working with old JQuery.
