I was working on a client site earlier today and needed to make a few changes, but when I clicked on the “Visual” tab in the editor WordPress acted as if nothing had happened.

Googling the issue led to a variety of solutions, the most common listed below:

1. Try to enable a default theme like Twenty Eleven or Twenty Twelve to quickly rule out any theme-specific issues
2. Disable all plugins to rule out any conflicting PHP issues
3. Try a different browser and/or computer to rule out caching problems

After the above suggested solutions didn’t work, I found a great post in the WordPress Forums which put the problem to rest.

1. Navigate via FTP or CPanel to your root WordPress installation
2. Open wp-config.php (for best practice, be sure to create a backup!)
3. In Notepad or my personal favorite Notepad++, press CTRL+F and search for /* That’s all, stop editing! Happy blogging. */
4. Copy and paste the following code directly above the “That’s all, stop editing! Happy blogging.” line:

   define('CONCATENATE_SCRIPTS', false);

This fix worked flawlessly for myself, I hope I was able to help a few of you out who were stuck like me!